# Sentinel

> Sentinel is a website and infrastructure monitoring platform for agencies and freelance developers. It monitors uptime, SSL certificates, DNS records, domain expiration, page keywords and JSON API responses from four global regions, with instant alerts and client-facing status pages. Checks are performed by SentinelBot, a Cloudflare-verified bot (listed in the Cloudflare Radar bots directory), so they are recognized as legitimate monitoring traffic rather than challenged; the user agent and monitoring IPs are documented at https://sentinel.rootstuff.io/bot.

## Product Pages

- [200 OK Explained](https://sentinel.rootstuff.io/http-status-codes/200): The request succeeded. This is the normal response for a healthy page or API.
- [301 Moved Permanently Explained](https://sentinel.rootstuff.io/http-status-codes/301): The resource has permanently moved to a new URL. Browsers and search engines should update to the new location.
- [302 Found Explained](https://sentinel.rootstuff.io/http-status-codes/302): The resource is temporarily at a different URL. Unlike a 301, clients keep using the original URL for future requests.
- [400 Bad Request Explained](https://sentinel.rootstuff.io/http-status-codes/400): The server could not understand the request, usually because it was malformed.
- [401 Unauthorized Explained](https://sentinel.rootstuff.io/http-status-codes/401): Authentication is required and has failed or not been provided.
- [403 Forbidden Explained](https://sentinel.rootstuff.io/http-status-codes/403): The server understood the request but refuses to authorize it. Unlike 401, authenticating will not help.
- [404 Not Found Explained](https://sentinel.rootstuff.io/http-status-codes/404): The server could not find the requested resource. The URL may be wrong or the resource may have been removed.
- [413 Payload Too Large Explained](https://sentinel.rootstuff.io/http-status-codes/413): The request body is larger than the server is willing or able to process, for example an oversized file upload.
- [415 Unsupported Media Type Explained](https://sentinel.rootstuff.io/http-status-codes/415): The request body is in a format the server does not support, for example sending XML to a JSON-only API.
- [418 I'm a Teapot Explained](https://sentinel.rootstuff.io/http-status-codes/418): An April Fools joke code from 1998: the server is a teapot and cannot brew coffee. Some sites return it as a playful block response.
- [422 Unprocessable Entity Explained](https://sentinel.rootstuff.io/http-status-codes/422): The request was well-formed but failed validation, for example a missing required field. Common in JSON APIs and Laravel.
- [429 Too Many Requests Explained](https://sentinel.rootstuff.io/http-status-codes/429): The client has sent too many requests in a given amount of time and is being rate limited.
- [451 Unavailable For Legal Reasons Explained](https://sentinel.rootstuff.io/http-status-codes/451): The resource is unavailable due to a legal demand, such as a government block or a takedown.
- [500 Internal Server Error Explained](https://sentinel.rootstuff.io/http-status-codes/500): A generic server-side error. Something failed on the server and it could not complete the request.
- [502 Bad Gateway Explained](https://sentinel.rootstuff.io/http-status-codes/502): A server acting as a gateway or proxy got an invalid response from the upstream server it was trying to reach.
- [503 Service Unavailable Explained](https://sentinel.rootstuff.io/http-status-codes/503): The server is temporarily unable to handle the request, usually because it is overloaded or down for maintenance.
- [504 Gateway Timeout Explained](https://sentinel.rootstuff.io/http-status-codes/504): A gateway or proxy did not get a timely response from the upstream server.
- [507 Insufficient Storage Explained](https://sentinel.rootstuff.io/http-status-codes/507): The server cannot store what is needed to complete the request, often a full disk.
- [525 SSL Handshake Failed Explained](https://sentinel.rootstuff.io/http-status-codes/525): A Cloudflare-specific code: the TLS handshake between Cloudflare and your origin failed.
- [Is facebook.com Down?](https://sentinel.rootstuff.io/is-it-down/facebook.com): Live status check for facebook.com: current reachability, response time and a free multi-region check. No signup required.
- [Is instagram.com Down?](https://sentinel.rootstuff.io/is-it-down/instagram.com): Live status check for instagram.com: current reachability, response time and a free multi-region check. No signup required.
- [Is whatsapp.com Down?](https://sentinel.rootstuff.io/is-it-down/whatsapp.com): Live status check for whatsapp.com: current reachability, response time and a free multi-region check. No signup required.
- [Is x.com Down?](https://sentinel.rootstuff.io/is-it-down/x.com): Live status check for x.com: current reachability, response time and a free multi-region check. No signup required.
- [Is tiktok.com Down?](https://sentinel.rootstuff.io/is-it-down/tiktok.com): Live status check for tiktok.com: current reachability, response time and a free multi-region check. No signup required.
- [Is snapchat.com Down?](https://sentinel.rootstuff.io/is-it-down/snapchat.com): Live status check for snapchat.com: current reachability, response time and a free multi-region check. No signup required.
- [Is reddit.com Down?](https://sentinel.rootstuff.io/is-it-down/reddit.com): Live status check for reddit.com: current reachability, response time and a free multi-region check. No signup required.
- [Is discord.com Down?](https://sentinel.rootstuff.io/is-it-down/discord.com): Live status check for discord.com: current reachability, response time and a free multi-region check. No signup required.
- [Is google.com Down?](https://sentinel.rootstuff.io/is-it-down/google.com): Live status check for google.com: current reachability, response time and a free multi-region check. No signup required.
- [Is youtube.com Down?](https://sentinel.rootstuff.io/is-it-down/youtube.com): Live status check for youtube.com: current reachability, response time and a free multi-region check. No signup required.
- [Is gmail.com Down?](https://sentinel.rootstuff.io/is-it-down/gmail.com): Live status check for gmail.com: current reachability, response time and a free multi-region check. No signup required.
- [Is outlook.com Down?](https://sentinel.rootstuff.io/is-it-down/outlook.com): Live status check for outlook.com: current reachability, response time and a free multi-region check. No signup required.
- [Is chatgpt.com Down?](https://sentinel.rootstuff.io/is-it-down/chatgpt.com): Live status check for chatgpt.com: current reachability, response time and a free multi-region check. No signup required.
- [Is openai.com Down?](https://sentinel.rootstuff.io/is-it-down/openai.com): Live status check for openai.com: current reachability, response time and a free multi-region check. No signup required.
- [Is claude.ai Down?](https://sentinel.rootstuff.io/is-it-down/claude.ai): Live status check for claude.ai: current reachability, response time and a free multi-region check. No signup required.
- [Is netflix.com Down?](https://sentinel.rootstuff.io/is-it-down/netflix.com): Live status check for netflix.com: current reachability, response time and a free multi-region check. No signup required.
- [Is spotify.com Down?](https://sentinel.rootstuff.io/is-it-down/spotify.com): Live status check for spotify.com: current reachability, response time and a free multi-region check. No signup required.
- [Is twitch.tv Down?](https://sentinel.rootstuff.io/is-it-down/twitch.tv): Live status check for twitch.tv: current reachability, response time and a free multi-region check. No signup required.
- [Is roblox.com Down?](https://sentinel.rootstuff.io/is-it-down/roblox.com): Live status check for roblox.com: current reachability, response time and a free multi-region check. No signup required.
- [Is steampowered.com Down?](https://sentinel.rootstuff.io/is-it-down/steampowered.com): Live status check for steampowered.com: current reachability, response time and a free multi-region check. No signup required.
- [Is epicgames.com Down?](https://sentinel.rootstuff.io/is-it-down/epicgames.com): Live status check for epicgames.com: current reachability, response time and a free multi-region check. No signup required.
- [Is disneyplus.com Down?](https://sentinel.rootstuff.io/is-it-down/disneyplus.com): Live status check for disneyplus.com: current reachability, response time and a free multi-region check. No signup required.
- [Is zoom.us Down?](https://sentinel.rootstuff.io/is-it-down/zoom.us): Live status check for zoom.us: current reachability, response time and a free multi-region check. No signup required.
- [Is slack.com Down?](https://sentinel.rootstuff.io/is-it-down/slack.com): Live status check for slack.com: current reachability, response time and a free multi-region check. No signup required.
- [Is github.com Down?](https://sentinel.rootstuff.io/is-it-down/github.com): Live status check for github.com: current reachability, response time and a free multi-region check. No signup required.
- [Is amazon.com Down?](https://sentinel.rootstuff.io/is-it-down/amazon.com): Live status check for amazon.com: current reachability, response time and a free multi-region check. No signup required.
- [Is paypal.com Down?](https://sentinel.rootstuff.io/is-it-down/paypal.com): Live status check for paypal.com: current reachability, response time and a free multi-region check. No signup required.
- [Features](https://sentinel.rootstuff.io/features): Every Sentinel monitoring capability in one place — uptime, SSL, DNS, keyword, API, ping, port, heartbeat and cron.
- [Pricing](https://sentinel.rootstuff.io/pricing): Simple, transparent monitoring plans. Start free, upgrade as you grow, 14-day free trial on paid plans.
- [Integrations](https://sentinel.rootstuff.io/integrations): Connect Sentinel to Slack, Discord, webhooks and the tools your team already uses.
- [Status Pages](https://sentinel.rootstuff.io/status-pages): Public and password-protected status pages that keep clients informed during incidents.
- [Mac Menu Bar App](https://sentinel.rootstuff.io/mac-app): A native macOS menu bar app showing every client site's status without opening a browser: online, degraded and offline counts at a glance, native notifications when a monitor changes state, and one-click access to any monitor. Free to download; it authenticates with a read-only API token, which every plan includes, the free plan too.
- [MCP for AI Assistants](https://sentinel.rootstuff.io/mcp): Connect Claude, ChatGPT and any MCP-compatible AI assistant to your monitoring over the open Model Context Protocol. Ask “is anything down?” in plain language, triage incidents and pause monitors with 26 built-in tools.
- [Uptime Monitoring](https://sentinel.rootstuff.io/uptime-monitoring): 24/7 uptime checks every 30 seconds from four global regions with instant alerts.
- [SSL Certificate Monitoring](https://sentinel.rootstuff.io/ssl-certificate-monitoring): Track SSL certificate expiry and chain issues, with alerts weeks before a cert lapses.
- [DNS Monitoring](https://sentinel.rootstuff.io/dns-monitoring): Watch A, AAAA, MX and NS records and detect unauthorized or accidental DNS changes.
- [Slack Website Monitoring](https://sentinel.rootstuff.io/integrations/slack): Downtime alerts in your Slack channels with the official Sentinel app: one-click install, a channel per client, severity routing per channel.
- [GitHub Deploy Markers](https://sentinel.rootstuff.io/integrations/github): Connect GitHub and every deploy is drawn on your uptime charts and cited beside incidents, with optional monitoring pauses while a deployment runs.
- [Terraform Uptime Monitoring](https://sentinel.rootstuff.io/integrations/terraform): Manage monitors and alert webhooks as code with the official Terraform provider: version-controlled, PR-reviewed, drift-detected monitoring.
- [Discord Website Monitoring](https://sentinel.rootstuff.io/integrations/discord): Rich-embed alerts to a Discord server, free on every plan, including ping and port checks for game servers.
- [Microsoft Teams Uptime Alerts](https://sentinel.rootstuff.io/integrations/microsoft-teams): Adaptive Card alerts to Teams channels via the modern Workflows webhook.
- [Webhook Alerts](https://sentinel.rootstuff.io/integrations/webhooks): Signed JSON to any endpoint: feed PagerDuty, dashboards, or your own automation.
- [Monitor Websites from Claude](https://sentinel.rootstuff.io/integrations/claude): Connect Claude over MCP: ask what is down, triage incidents, manage monitors in conversation.
- [Keyword Monitoring](https://sentinel.rootstuff.io/keyword-monitoring): Verify expected text appears on a page, or detect defacement and error messages.
- [Server Error Detection](https://sentinel.rootstuff.io/server-error-monitoring): Detect PHP warnings, WordPress critical errors, SQL errors, and stack traces rendering on otherwise healthy pages. Zero configuration, every plan.
- [API Monitoring](https://sentinel.rootstuff.io/api-monitoring): Send custom HTTP requests and assert on the JSON response body to catch silent API failures behind a 200 OK.
- [Ping Monitoring](https://sentinel.rootstuff.io/ping-monitoring): ICMP echo from every region with multi-region consensus. For servers, network devices and anything that does not speak HTTP.
- [TCP Port Monitoring](https://sentinel.rootstuff.io/port-monitoring): TCP connection checks for databases, mail, SSH and any custom service listening on a port. Multi-region consensus, categorized failure reasons.
- [Heartbeat Monitoring](https://sentinel.rootstuff.io/heartbeat-monitoring): Push-based dead-man's-switch monitoring for cron jobs, backups and background workers. Your job pings a URL; a missing ping opens an incident.
- [Cron Job Monitoring](https://sentinel.rootstuff.io/cron-monitoring): Monitor scheduled cron jobs against their own cron expression and timezone. Get alerted the moment a scheduled run is missed or fails.
- [Domain Expiration Monitoring](https://sentinel.rootstuff.io/domain-expiration-monitoring): Never miss a domain renewal — get alerted well before a domain registration expires.
- [Response Time Monitoring](https://sentinel.rootstuff.io/response-time-monitoring): Track latency from multiple regions and spot performance regressions before users do.
- [Multi-Region Monitoring](https://sentinel.rootstuff.io/multi-region-monitoring): Check from four regions and require consensus to cut false alarms from regional blips.
- [Uptime Reports](https://sentinel.rootstuff.io/uptime-reports): Scheduled and on-demand uptime reports you can share with clients and stakeholders.
- [Incident Management](https://sentinel.rootstuff.io/incident-management): Automatic incident timelines, root-cause detail and resolution notes for every outage.
- [Website Monitoring for Agencies](https://sentinel.rootstuff.io/website-monitoring-for-agencies): Centralized monitoring for agencies managing dozens or hundreds of client websites.
- [WordPress Website Monitoring](https://sentinel.rootstuff.io/website-monitoring-for-wordpress): Monitoring built for WordPress sites — uptime, SSL, plugins-induced outages and more.
- [E-commerce Website Monitoring](https://sentinel.rootstuff.io/website-monitoring-for-ecommerce): Protect checkout, inventory and payment flows with monitoring tuned for online stores.
- [SaaS Website Monitoring](https://sentinel.rootstuff.io/website-monitoring-for-saas): Monitor SaaS apps and their health-check and API endpoints from four global regions.
- [Uptime Monitoring for Agencies](https://sentinel.rootstuff.io/uptime-monitoring-for-agencies): Uptime monitoring for digital agencies. Watch every client site from one dashboard, prove uptime with branded reports and status pages, and get alerted before clients notice.
- [Uptime Monitoring for Freelancers](https://sentinel.rootstuff.io/uptime-monitoring-for-freelancers): Affordable uptime monitoring for freelance developers and designers. Start free, get alerted before clients notice downtime, and look more professional.
- [Uptime Monitoring for SaaS](https://sentinel.rootstuff.io/uptime-monitoring-for-saas): Uptime monitoring for SaaS products. Track SLA targets, monitor API and health-check endpoints from four regions, alert on-call, and reduce churn with a public status page.
- [Sentinel vs StatusCake](https://sentinel.rootstuff.io/sentinel-vs-statuscake): How Sentinel compares to StatusCake for agency website monitoring — per-minute checks, bundled DNS/ping/port/heartbeat, branded status pages and automated client reports.
- [Sentinel vs UptimeRobot](https://sentinel.rootstuff.io/sentinel-vs-uptimerobot): How Sentinel compares to UptimeRobot after the August 2026 price increase — flat pricing with no SMS credit packs or per-seat fees, commercial-use free tier, and automated client reports.
- [Sentinel vs Pingdom](https://sentinel.rootstuff.io/sentinel-vs-pingdom): How Sentinel compares to Pingdom — simple flat tiers instead of usage-based pricing, a free-forever tier, and agency-focused status pages and reports.
- [Sentinel vs Better Stack](https://sentinel.rootstuff.io/sentinel-vs-betterstack): How Sentinel compares to Better Stack — monitoring built for agencies without on-call, log-management or per-responder pricing overhead.
- [Sentinel vs Uptime Kuma](https://sentinel.rootstuff.io/sentinel-vs-uptimekuma): A hosted alternative to Uptime Kuma — the real cost of self-hosting (time, maintenance, single-region, single point of failure) versus fully managed monitoring with multi-region checks, a REST API and MCP for AI assistants.
- [Sentinel vs Oh Dear](https://sentinel.rootstuff.io/sentinel-vs-ohdear): How Sentinel compares to Oh Dear: every check verified from four regions instead of one primary location, flat plan pricing instead of per-site tiers, and a free-forever tier Oh Dear doesn't offer.
- [Downtime Cost Calculator](https://sentinel.rootstuff.io/tools/downtime-cost-calculator): Free calculator that estimates what an outage costs in lost revenue and staff time. No signup required.
- [Uptime SLA Calculator](https://sentinel.rootstuff.io/tools/uptime-sla-calculator): Free calculator that converts any SLA uptime percentage into allowed downtime per day, week, month and year, and back. No signup required.
- [SSL & TLS Checker](https://sentinel.rootstuff.io/tools/ssl-checker): Free SSL checker: certificate validity, issuer and expiry countdown plus the negotiated TLS protocol, cipher and an A-to-F security grade. No signup required.
- [DNS Lookup](https://sentinel.rootstuff.io/tools/dns-lookup): Free DNS lookup for any domain: A, AAAA, CNAME, MX, NS, TXT and SOA records with TTLs. No signup required.
- [HTTP Header Checker](https://sentinel.rootstuff.io/tools/http-header-checker): Free HTTP header checker: status code, redirect count and full response headers with a security-header checklist. No signup required.
- [Domain Expiry Checker](https://sentinel.rootstuff.io/tools/domain-expiry-checker): Free WHOIS domain expiry lookup: registrar, creation and expiration dates, transfer-lock status and nameservers. No signup required.
- [Website Speed Test (Multi-Region)](https://sentinel.rootstuff.io/tools/website-speed-test): Free website speed test from multiple monitoring regions at once: DNS, TCP, TLS and time-to-first-byte for each location. No signup required.
- [Is It Down? Live Site Status Checker](https://sentinel.rootstuff.io/is-it-down): Check whether any website is down right now, verified from a real monitoring network rather than a single location. No signup required.
- [DNS Propagation Checker](https://sentinel.rootstuff.io/tools/dns-propagation-checker): Check whether a DNS change has propagated by querying multiple major public resolvers at once and comparing their answers. No signup required.
- [Redirect Checker](https://sentinel.rootstuff.io/tools/redirect-checker): Trace a URL's full redirect chain, every 301 and 302 hop to the final destination, with the status code at each step. No signup required.
- [Cron Expression Builder](https://sentinel.rootstuff.io/tools/cron-expression-builder): Build and decode cron expressions in plain English and preview the next scheduled run times. No signup required.
- [Website Health Check](https://sentinel.rootstuff.io/tools/website-health-check): A free all-in-one website audit: HTTPS and TLS, security and cache headers, HTTP/2 and HTTP/3, DNS, IPv6, DNSSEC, domain expiry, robots and sitemap, graded in one report. No signup required.
- [AI Readiness Check](https://sentinel.rootstuff.io/tools/ai-readiness-check): Check whether your site is ready for AI agents: can they reach it (robots.txt AI-crawler rules, no bot wall), read it without running JavaScript, and use its agent signals (llms.txt, structured data, sitemap, MCP, x402 payment manifest). Graded in one report. No signup required.
- [Agent-Payable Services Directory](https://sentinel.rootstuff.io/agents/directory): A curated directory of live services AI agents can discover and pay per call via x402 and the Machine Payments Protocol, organized by the capability gap each fills. Every listing is verified alive by a Sentinel monitor.
- [HTTP Status Codes Explained](https://sentinel.rootstuff.io/http-status-codes): A plain-English reference for every HTTP status code: what it means, what causes it and how to fix it, from 200 OK to 500, 502, 503 and 504.

## AI Agents (MCP)

Sentinel is built to be operated by AI agents. It exposes an MCP (Model Context Protocol) server over Streamable HTTP at https://sentinel.rootstuff.io/mcp/sentinel with 25 tools: uptime summaries, monitor, incident, and group CRUD, performance and DNS history, SSL certificate expiry, and on-demand global URL checks.

- Authenticate with an API token (Authorization: Bearer header), created at https://sentinel.rootstuff.io/user/api-tokens, or via OAuth 2.1 with dynamic client registration at https://sentinel.rootstuff.io/mcp/sentinel-oauth.
- API and MCP access is included on every plan: read-only tools on Free and Starter (on-demand global URL checks require a paid plan), full read/write on Pro and Business.
- Token permissions (read, create, update, delete) are enforced, so an autonomous agent can be given a read-only or otherwise scoped credential.
- [Connecting AI Assistants (MCP)](https://sentinel.rootstuff.io/docs/mcp): setup guide for Claude and other MCP clients
- [MCP Tools Reference](https://sentinel.rootstuff.io/docs/mcp-tools): every tool with its inputs and outputs
- [REST API reference](https://sentinel.rootstuff.io/docs/api-access): the same capabilities over plain HTTP
- [Agent-Payable Services Directory (JSON)](https://sentinel.rootstuff.io/agents/directory.json): machine-readable mirror of the directory, every listing with its live verification status in one request
- [Agent-Payable Services Directory (llms.txt)](https://sentinel.rootstuff.io/agents/directory/llms.txt): the same directory as plain text
- [Paid global check, no account needed](https://sentinel.rootstuff.io/mpp/): agents pay $0.02 in USDC per call and get a four-region consensus check of any URL with per-region latency and a receipt. Two payment rails, both settled via Stripe: MPP (USDC on Tempo) at POST https://sentinel.rootstuff.io/mpp/check, and x402 (USDC on Base) at POST https://sentinel.rootstuff.io/x402/check with the manifest at https://sentinel.rootstuff.io/.well-known/x402. Send {"url": "..."}; the first call returns an HTTP 402 payment challenge. Discovery document at https://sentinel.rootstuff.io/mpp/openapi.json.

## Documentation

- [Introduction](https://sentinel.rootstuff.io/docs/introduction)
- [Quick Start](https://sentinel.rootstuff.io/docs/quick-start)
- [Website Monitoring](https://sentinel.rootstuff.io/docs/website-monitoring)
- [SSL Certificates](https://sentinel.rootstuff.io/docs/ssl-certificates)
- [DNS Monitoring](https://sentinel.rootstuff.io/docs/dns-monitoring)
- [Keyword Monitoring](https://sentinel.rootstuff.io/docs/keyword-monitoring)
- [Server Error Detection](https://sentinel.rootstuff.io/docs/error-detection)
- [API Monitoring](https://sentinel.rootstuff.io/docs/api-monitoring)
- [Ping Monitoring](https://sentinel.rootstuff.io/docs/ping-monitoring)
- [Port Monitoring](https://sentinel.rootstuff.io/docs/port-monitoring)
- [Heartbeat Monitoring](https://sentinel.rootstuff.io/docs/heartbeat-monitoring)
- [Cron Job Monitoring](https://sentinel.rootstuff.io/docs/cron-monitoring)
- [Notifications](https://sentinel.rootstuff.io/docs/notifications)
- [Status Pages](https://sentinel.rootstuff.io/docs/status-pages)
- [Uptime Reports](https://sentinel.rootstuff.io/docs/uptime-reports)
- [Team Management](https://sentinel.rootstuff.io/docs/team-management)
- [API Access](https://sentinel.rootstuff.io/docs/api-access)
- [CLI](https://sentinel.rootstuff.io/docs/cli)
- [Slack Integration](https://sentinel.rootstuff.io/docs/slack)
- [Discord Integration](https://sentinel.rootstuff.io/docs/discord)
- [Microsoft Teams Integration](https://sentinel.rootstuff.io/docs/teams)
- [Webhooks](https://sentinel.rootstuff.io/docs/webhooks)
- [GitHub Deploys](https://sentinel.rootstuff.io/docs/github)
- [Terraform Provider](https://sentinel.rootstuff.io/docs/terraform)
- [Connecting AI Assistants (MCP)](https://sentinel.rootstuff.io/docs/mcp)
- [MCP Tools Reference](https://sentinel.rootstuff.io/docs/mcp-tools)
- [CI/CD & Pausing Monitors](https://sentinel.rootstuff.io/docs/cicd-pause-monitoring)
- [Import & Export](https://sentinel.rootstuff.io/docs/import-export)
- [Troubleshooting](https://sentinel.rootstuff.io/docs/troubleshooting)

## Blog

- [What I Learned Running laravel/mcp in Production](https://sentinel.rootstuff.io/blog/laravel-mcp-in-production): An engineering write-up of Sentinel's production MCP server on laravel/mcp: tool and schema design, running bearer and OAuth front doors off one server class, plan-aware authorization, per-tool usage logging, and the dependency gotcha that 404'd every MCP route in production.
- [What Can an AI Agent Actually Buy? I Made a List](https://sentinel.rootstuff.io/blog/what-can-an-ai-agent-actually-buy): Introducing the Sentinel Agent Directory: a curated index of services AI agents can discover and pay for per call over x402 and the Machine Payments Protocol. Every listing is probed by a live monitor, so the directory proves its entries are alive.
- [Sentinel Is Now on the Slack Marketplace](https://sentinel.rootstuff.io/blog/sentinel-slack-marketplace): The official Sentinel Slack app is now on the Slack Marketplace: down and recovery alerts in your channels, per-channel installs with severity filtering, reviewed and approved by Slack. Available on every paid plan.
- [Sentinel Now Detects PHP Errors, Stack Traces, and Server Warnings Automatically](https://sentinel.rootstuff.io/blog/detect-server-errors-automatically): Sentinel now automatically detects PHP errors, stack traces, WordPress critical errors, SQL errors, and framework debug pages during normal HTTP monitoring. No keyword lists to maintain, included on every plan.
- [Your Host Monitors Their Server, Not Your Site](https://sentinel.rootstuff.io/blog/your-host-monitors-their-server): Hosting companies monitor their servers for their own SLA. Why that is not uptime monitoring: expired certificates, DNS mistakes, broken deploys, and independent evidence when a client asks how long the site was down.
- [Your Uptime Chart Should Know When You Deployed](https://sentinel.rootstuff.io/blog/deploy-markers-uptime-charts): Every incident starts with the same question: did we just ship? Deploy markers draw the answer directly on the response-time chart, cite deploys beside incidents, and can pause monitoring while a deployment runs.
- [Discord Alerts Are Now Free for Everyone](https://sentinel.rootstuff.io/blog/free-discord-uptime-alerts): Slack is a business signal and Discord is a hobbyist signal, so gating Discord monetized nobody. The reasoning behind the pricing change, and what the free plan includes now.
- [One Permission Is Enough: How We Build Integrations](https://sentinel.rootstuff.io/blog/one-permission-is-enough): Our Slack app asks for one scope. Our GitHub app holds no credentials at all. Why minimal permissions shaped what got built, what that constraint costs, and why the consent screen is part of the product.
- [Your Site Can Return 200 and Still Be Down](https://sentinel.rootstuff.io/blog/website-returns-200-but-is-down): A status code tells you the server answered, not that it answered with your website. Why managed hosts serve error pages at 200, and why a keyword check that asserts your headline is present beats one that hunts for the word "error".
- [Your Monitoring Dashboard Is a Tab You Never Open](https://sentinel.rootstuff.io/blog/monitoring-dashboard-you-never-open): Alerts tell you when something changes. They cannot tell you that nothing has, which is the failure agencies actually fear. Why passive awareness beats another dashboard, and where a menu bar app fits.
- [Monitoring for AI-Built Apps: The Ops Habit Vibe Coders Skip](https://sentinel.rootstuff.io/blog/monitoring-for-ai-built-apps): AI can write your app in an afternoon, but it won't tell you when it's down. Why vibe-coded apps need uptime, SSL, and heartbeat monitoring, and how to add it in minutes.
- [UptimeRobot's Free Plan Bans Commercial Use: Are Your Client Monitors in Violation?](https://sentinel.rootstuff.io/blog/uptimerobot-free-plan-commercial-use): Since a November 2024 ToS change, UptimeRobot's free plan is for non-commercial use only. If you monitor client sites on it, here's what that means and your options.
- [Freshping Alternatives in 2026: Free & Paid Options After the Shutdown](https://sentinel.rootstuff.io/blog/freshping-alternatives): Freshping shut down in March 2026. Here are honest alternatives (Uptime Kuma, UptimeRobot, HetrixTools, and Sentinel) compared for freelancers and agencies monitoring client sites.
- [SentinelBot Is Now a Cloudflare Verified Bot](https://sentinel.rootstuff.io/blog/sentinelbot-cloudflare-verified-bot): Sentinel's monitoring crawler is listed in Cloudflare's Radar bots directory. What SentinelBot does, what verification means for false "down" alerts on Cloudflare-protected sites, and how site owners stay in control.
- [How Much to Charge for Website Maintenance (2026 Guide)](https://sentinel.rootstuff.io/blog/how-much-to-charge-for-website-maintenance): The three pricing models for website maintenance, typical 2026 retainer ranges by tier, and why the most persuasive price is anchored to what downtime costs the client, not what the work costs you.
- [Client-Down Email Templates: What to Send When a Client Site Goes Offline](https://sentinel.rootstuff.io/blog/client-website-down-email-templates): Three copy-paste email templates for client outages: the fast initial notification, the mid-incident update, and the all-clear wrap-up that turns a bad afternoon into renewed trust.
- [Monthly Uptime Report Template for Agencies and Freelancers](https://sentinel.rootstuff.io/blog/monthly-uptime-report-template): A copyable seven-section structure for monthly client uptime reports, plus the three rules that make them land: send them even when nothing happened, use real numbers, automate the data.
- [Sentinel Is Now in the Official MCP Registry](https://sentinel.rootstuff.io/blog/sentinel-official-mcp-registry): Sentinel is listed in the official MCP Registry as io.rootstuff/sentinel: a verified, first-party server that lets Claude, ChatGPT, and any MCP client operate your monitoring in plain language.
- [How to Tell If Your Website Has Been Hacked: 9 Warning Signs](https://sentinel.rootstuff.io/blog/how-to-tell-if-your-website-is-hacked): Most hacked websites don't look hacked. The nine warning signs of a compromised site, how to confirm it, what to do right now, and the external checks that catch the next one in minutes.
- [Website Defacement: How to Detect It in Minutes, Not Days](https://sentinel.rootstuff.io/blog/website-defacement-monitoring): What website defacement is (from full page takeovers to hidden spam and cloaked redirects), why detection speed decides the damage, and how to set up content checks that catch it fast.
- [What Happens When a Domain Expires (and How to Never Let It Happen)](https://sentinel.rootstuff.io/blog/what-happens-when-a-domain-expires): The domain expiration timeline stage by stage, why a dropped domain is a security incident and not just an outage, and the monitoring layer that catches silent auto-renew failures.
- [Open-Source Uptime Monitoring Tools (2026): Self-Hosted Options Compared](https://sentinel.rootstuff.io/blog/open-source-uptime-monitoring-tools): The best open-source uptime monitoring tools in 2026: Uptime Kuma, Gatus and more, what they do well, and the honest cost of self-hosting before you commit.
- [Uptime Monitoring Tools With an API, and Now MCP for AI Assistants](https://sentinel.rootstuff.io/blog/uptime-monitoring-tools-with-api): Why an API changes what monitoring can do, what to look for, and the new layer: MCP, which lets AI assistants like Claude and ChatGPT query your monitoring in plain language.
- [Affordable Uptime Monitoring Tools That Don't Cut Corners](https://sentinel.rootstuff.io/blog/affordable-uptime-monitoring-tools): How to find genuinely affordable uptime monitoring: the pricing models that stay cheap, the hidden costs that make "cheap" expensive, and how the budget options really compare.
- [The Best Pingdom Alternatives in 2026 (Compared by Use Case)](https://sentinel.rootstuff.io/blog/pingdom-alternatives): Looking for a Pingdom alternative? Why teams switch, the criteria that actually decide the right tool, and how the main alternatives compare for free trackers, dev platforms and agencies.
- [The Best UptimeRobot Alternatives in 2026 (and How to Choose One)](https://sentinel.rootstuff.io/blog/uptimerobot-alternatives): Outgrowing UptimeRobot? Why teams move on, the criteria that actually matter, and how the main alternatives compare across free trackers, developer platforms and agency tools.
- [The Best Status Page Software in 2026 (and How to Choose One)](https://sentinel.rootstuff.io/blog/best-status-page-software): Skip the rankings. What a status page is really for, the criteria that decide the right tool, the three categories of status page software, and what to test before you commit.
- [Shopify Uptime Monitoring: Why Your Store Still Goes Down (and What to Watch)](https://sentinel.rootstuff.io/blog/shopify-uptime-monitoring): Shopify being up does not mean your store is working. Why Shopify stores still go down, what to actually monitor beyond the homepage, and how to catch problems before they cost sales.
- [The Best Uptime Monitoring Tools in 2026 (and How to Choose One)](https://sentinel.rootstuff.io/blog/best-uptime-monitoring-tools): Skip the cookie-cutter rankings. The criteria and categories that actually decide the best uptime monitoring tool for you, from free trackers to agency platforms, plus how the popular names compare.
- [Free Uptime Monitoring: What You Get, What You Don't, and When to Upgrade](https://sentinel.rootstuff.io/blog/free-uptime-monitoring): What free uptime monitoring actually covers, where free plans draw the line, how to set up solid monitoring without paying, and when upgrading finally earns its keep.
- [How to Monitor Website Uptime: A Step-by-Step Guide](https://sentinel.rootstuff.io/blog/how-to-monitor-website-uptime): A practical, step-by-step guide to setting up website uptime monitoring: what to monitor, how often to check, where to check from, alerts that don't cry wolf, and how to prove uptime.
- [How to Choose Uptime Monitoring Software for Your Agency (2026 Buyer's Guide)](https://sentinel.rootstuff.io/blog/choosing-uptime-monitoring-for-agencies): The criteria that actually matter when an agency picks a monitoring tool: multi-client organization, alert routing, white-label branding, reporting, check types and a pricing model that scales.
- [How to Onboard a New Client to Uptime Monitoring (An Agency Checklist)](https://sentinel.rootstuff.io/blog/agency-monitoring-onboarding-checklist): A repeatable, twenty-minute checklist for adding every new client to monitoring: what to gather, which monitors to add, naming and tagging, alert routing, status pages and the email that proves your value.
- [White-Label Uptime Monitoring: How Agencies Rebrand Monitoring as Their Own Service](https://sentinel.rootstuff.io/blog/white-label-uptime-monitoring): Turn monitoring from an invisible cost into a branded, billable service: branded status pages on custom domains, white-labeled client reports, on-brand alerting, and the economics of reselling it.
- [API Monitoring: How to Monitor REST APIs and Catch Failures Before Users Do](https://sentinel.rootstuff.io/blog/api-monitoring-guide): A practical guide to API monitoring: what to check beyond a 200, how to assert JSON payloads, alerting that doesn't cry wolf, and when synthetic flows beat single endpoints.
- [What Does 99.9% Uptime Actually Mean? (Plus the Five-Nines Cheat Sheet)](https://sentinel.rootstuff.io/blog/what-does-99-9-uptime-mean): What 99%, 99.9%, 99.99% and 99.999% uptime actually translate to in real downtime, plus how SLAs are calculated and what's realistic to promise clients.
- [Synthetic Monitoring vs Real User Monitoring: What's the Difference?](https://sentinel.rootstuff.io/blog/synthetic-monitoring-vs-real-user-monitoring): Synthetic monitoring and real user monitoring (RUM) sound similar but answer different questions. What each one does, where each one fails, and which you need first.
- [The Complete Guide to Uptime Monitoring in 2026](https://sentinel.rootstuff.io/blog/complete-guide-to-uptime-monitoring): Everything you need to know about uptime monitoring in 2026: the five check types, KPIs that matter, alert strategies that don't cry wolf, and how to pick the right tool.
- [Global Uptime Monitoring: Why Multi-Region Checks Matter](https://sentinel.rootstuff.io/blog/global-uptime-monitoring): Why single-region monitoring misses real outages, how multi-region checks catch regional failures, and what to look for in a global uptime tool.
- [How Much Does Website Monitoring Cost? A 2026 Pricing Breakdown](https://sentinel.rootstuff.io/blog/how-much-does-website-monitoring-cost): A clear breakdown of website monitoring pricing models, what drives cost, sample budgets for 5, 50, and 500 sites, and when paid plans pay for themselves.
- [How to Monitor Multiple Websites from One Dashboard](https://sentinel.rootstuff.io/blog/monitor-multiple-websites): Learn how to monitor dozens or hundreds of websites from a single dashboard with organized alerts, team permissions, and per-client status pages.
- [How to Reduce Website Downtime: 10 Proven Strategies](https://sentinel.rootstuff.io/blog/how-to-reduce-website-downtime): 10 actionable strategies to reduce website downtime, from external monitoring and DNS redundancy to staging environments and incident runbooks.
- [How to Build a Website Care Plan That Clients Will Pay For](https://sentinel.rootstuff.io/blog/website-care-plan-for-clients): A step-by-step guide to building website care plans with tiered pricing, monitoring, reporting, and strategies that turn maintenance into recurring revenue.
- [WordPress Uptime Monitoring: How to Keep Your Site Online 24/7](https://sentinel.rootstuff.io/blog/wordpress-uptime-monitoring): A practical guide to WordPress uptime monitoring: why WP sites go down, what to monitor, and how to set up external monitoring that actually catches problems.
- [Why Is My Website Down? A Non-Technical Guide to Diagnosing and Fixing It](https://sentinel.rootstuff.io/blog/why-is-my-website-down): A non-technical, step-by-step guide to diagnosing why your website is down, what to do right now, and how to make sure it never happens by surprise again.
- [The Freelancer's Guide to Monitoring Client Websites (Without Getting Overwhelmed)](https://sentinel.rootstuff.io/blog/freelance-website-monitoring-guide): A practical monitoring playbook for freelance web developers: minimum viable stack, alert triage, a 30-minute setup, and how to charge for uptime as a retainer.
- [How to Create an Uptime SLA for Client Websites](https://sentinel.rootstuff.io/blog/uptime-sla-for-client-websites): Learn how to define uptime guarantees, set realistic targets, and use monitoring data to back up your SLA commitments to clients.
- [The True Cost of Website Downtime (And How to Calculate It)](https://sentinel.rootstuff.io/blog/website-downtime-cost): Learn how to calculate the true cost of website downtime, including hidden costs like SEO damage and lost trust. Protect your revenue with proactive monitoring.
- [Website Monitoring for Agencies: The Complete Guide](https://sentinel.rootstuff.io/blog/website-monitoring-for-agencies): A complete guide to website monitoring for agencies. Learn how to manage client sites, organize alerts, and prove your value with uptime reports.
- [How to Set Up a Public Status Page for Your Clients](https://sentinel.rootstuff.io/blog/how-to-set-up-status-page): Learn how to set up a public status page that builds client trust, reduces support tickets, and communicates incidents transparently.
- [SSL Certificate Expiration: What Happens and How to Prevent It](https://sentinel.rootstuff.io/blog/ssl-certificate-expiration-prevention): Discover what happens when SSL certificates expire, how it impacts your site, and how automated monitoring prevents certificate-related outages.
- [Uptime Monitoring Explained: What It Is and How to Get Started](https://sentinel.rootstuff.io/blog/uptime-monitoring-explained): Everything you need to know about uptime monitoring: how it works, why check intervals matter, and how to set it up in 60 seconds.
- [DNS Monitoring: Protecting Your Domain from Hijacking and Outages](https://sentinel.rootstuff.io/blog/dns-monitoring-guide): Learn how DNS monitoring works, what records to watch, and how to protect your domain from hijacking, unauthorized changes, and outages.
- [Incident Management for Web Teams: From Alert to Resolution](https://sentinel.rootstuff.io/blog/incident-management-guide): A practical guide to incident management for web teams. Learn the incident lifecycle, escalation workflows, and how to reduce mean time to resolution.
- [7 Website Monitoring Best Practices Every Agency Should Follow](https://sentinel.rootstuff.io/blog/website-monitoring-best-practices): Seven practical website monitoring best practices for agencies, from multi-region checks to CI/CD integration and smart alerting strategies.

## Company

- [About](https://sentinel.rootstuff.io/about): Who builds Sentinel and why — a monitoring tool by rootstuff for the people who ship the web.
- [Brand](https://sentinel.rootstuff.io/brand): The Sentinel brand: the two-tone shield mark, the paper and carbon palettes, typography, and usage guidelines.
- [Contact](https://sentinel.rootstuff.io/contact): Get in touch with the Sentinel team for support, sales or beta access.

## Optional

- [Full blog content](https://sentinel.rootstuff.io/llms-full.txt): the complete text of every Sentinel blog article in one file