Best Uptime Monitoring for Agencies in 2026

Disclosure first. I run Sentinel, and it's ranked first below. To keep the ranking honest, every tool gets the same numbers next to it: what it costs for 100 monitors on monthly billing, how many places it checks from, and what it leaves out. Judge by those, not by who wrote this. Prices were read from each vendor's pricing page on September 30, 2026 and will drift; check before you buy.

At a glance

• Best overall for agencies: Sentinel. Every check verified from four regions before it alerts, all check types on the free plan, groups as clients, no seat fees on Business. $29 a month for 100 monitors.
• Biggest free tier: UptimeRobot. 50 monitors at five-minute checks for nothing. Paid plans add seat fees.
• Cheapest paid plan: Notifier. $19 a month for 100 monitors at 30-second checks. Single-location checks by default.
• Best for incident workflows: Better Stack. Monitoring, on-call and incident management in one tool. Status pages get expensive at agency scale.
• Per-site agency pricing: Oh Dear. Unlimited users on every plan, priced per site. $165 a month for 50 sites.
• Best self-hosted: Uptime Kuma. Free and good, and now your monitoring runs on a box you maintain.

What an agency actually needs from monitoring

Monitoring one site is easy. Monitoring 40 client sites for money is a different product, and most "best uptime tools" lists are written for the first case. Here's what the second one requires.

• Two to five monitors per site. Homepage, login or checkout, the SSL certificate, the domain's expiry date, maybe a keyword on the page that proves the CMS rendered. A 50-client roster is 100 to 250 monitors, so price every tool at that scale, not at ten.
• A status page per client, ideally on the client's own domain. It cuts "is the site down?" emails and it's a deliverable you can point to in the retainer.
• Seats that don't cost extra. Your project manager, your developer and your support person all need to see the dashboard. Per-seat pricing turns a $39 plan into a $96 plan.
• Alert routing per client. The client's Slack channel, the account manager's phone, your on-call rotation. One firehose to one inbox doesn't survive 40 clients.
• Reports you can put your name on. A monthly uptime report with your logo is how monitoring stops being an invisible cost and starts justifying the maintenance fee.
• More than uptime. Expired certificates and lapsed domains cause more client emergencies than servers falling over, and neither one shows up on a plain HTTP check.
• Checks verified from more than one place. A monitor that checks from a single location will page you at 3am about a routing hiccup between one datacenter and one host. When you're monitoring other people's sites, false alerts don't just cost sleep; they cost credibility with the client you woke up.

That last point is the one most lists skip, and it's the reason the first-place tool below is the one it is.

The six tools, ranked

1. Sentinel (best overall for agencies)

Sentinel is the only tool on this list that checks every monitor from four regions at once and alerts only when they agree. Virginia, Oregon, Germany and Singapore, every check, every plan, including free. The practical effect is that an alert from Sentinel means the site is down, not that one probe had a bad route.

Pricing is flat. Free is 10 monitors at five-minute checks with every check type except heartbeat and cron included: uptime, SSL expiry, DNS changes, domain expiry, ping, port, keyword and JSON. Client work is explicitly allowed. Starter is $14 a month for 25 monitors at one-minute checks and five status pages. Pro is $29 for 100 monitors, 10 status pages on your own domains, five team seats and full API access. Business is $79 for 300 monitors at 30-second checks, unlimited seats, unlimited status pages, white-label monthly reports, and PagerDuty.

The agency features are built in rather than bolted on. Monitors live in groups, and a group is a client: it carries its own alert routing, its own status page, its own report. Alerts go to email, Slack (an official Marketplace app, not a pasted webhook), Discord, Microsoft Teams, Telegram, PagerDuty and webhooks. Deploys from GitHub are drawn on the response-time charts so you can see which release broke what.

What's missing: the free tier is 10 monitors, not 50, so it's a trial-sized tier rather than a place to park a client roster. Thirty-second checks and white-label reports sit on the $79 plan; at $29 you get one-minute checks and Sentinel's name on the report footer. There's no phone-call alerting.

Pick it if you're responsible for other people's sites and you want alerts you don't have to second-guess. Start free and move ten client sites over to see how it feels.

2. UptimeRobot (biggest free tier)

UptimeRobot's free plan is still the most generous in the category, and its paid plans are where the agency math turns against you. Free is 50 monitors at five-minute checks with one status page. That's enough to monitor a small roster without paying anything, which is why so many agencies have.

Two things to know before you build on it. First, the free plan spent most of the past year under in-app "non-commercial use only" compliance notices. UptimeRobot rewrote its terms in May 2026 to allow any use, then replaced the ban with a fair-use policy whose stated remedy for an account review is moving to the plan that matches your usage. I wrote up the whole sequence. Second, the paid plans price seats separately. Team is $46 a month for 100 monitors at 30-second checks with three seats included and $19 for each seat after that. A five-person agency is $84 before the annual discount.

Checks run from one location per check, rotating, and re-checks come from that same location. Solo is $13 a month for 10 monitors at one-minute checks.

Pick it if your roster fits in 50 monitors and you're comfortable that the free plan's terms have already moved once.

3. Notifier (cheapest paid plan)

Notifier's Team plan is $19 a month for 100 monitors at 30-second checks, which makes it the cheapest paid option here by a wide margin. Three seats and 50 status pages are included, custom domains for status pages start on the $4 Solo plan, and the free tier is 10 monitors at five-minute checks with commercial use allowed. It's bootstrapped and run by one founder, and by its own account has been monitoring since 2018.

The gap is verification. Notifier's own guide on multi-location monitoring says the feature is "currently in beta and available to all Notifier users on request," and doesn't say how many locations that involves. By default your monitors are checked from one place, and a single-location check is the kind that pages you about problems the client's visitors never saw. There's no documented white-label option for status pages or reports.

Pick it if price per monitor is the deciding factor and you'll accept occasional false alerts as the cost.

4. Better Stack (incident workflows)

Better Stack is the tool to choose when you want on-call schedules and incident management in the same place as the monitors. Uptime monitoring, an alerting and escalation layer, incident timelines and log management share one account, and the monitoring side is solid: checks as often as every 30 seconds, keyword and TCP checks, multi-location verification.

Pricing is modular, and modular pricing bites at agency scale. The free plan is 10 monitors and one status page. Monitors are then sold in blocks of 50 for $25 a month each, so 100 monitors is roughly $50. Additional status pages are $15 a month each; a status page per client for 30 clients is $435 a month before you've bought a monitor.

Pick it if your agency runs a real on-call rotation and wants incidents managed where the alerts are born. Skip it if the deliverable is a status page per client.

5. Oh Dear (per-site agency pricing)

Oh Dear prices by site rather than by monitor, and every plan includes unlimited users. Each site gets uptime, certificate, broken-link, mixed-content, DNS, scheduled-task and performance checks in one bundle, plus a status page with subscriber notifications. It's built by a small team in Belgium that's been at it for years, and the product is polished.

The price is the conversation. The Agency plan is $165 a month for 50 sites, Studio is $109 for 25, and Freelance is $55 for 10. There's a 10-day trial and no free plan. Checks come from one primary location with a second location verifying a failure before it alerts, which is better than single-location and less than four.

Pick it if you'd rather pay per site and get every check type per site without configuring monitors individually, and $3 a site fits inside the retainer.

6. Uptime Kuma (self-hosted)

Uptime Kuma is free, open source, genuinely good, and it turns your monitoring into a server you're responsible for. Docker up, add monitors, connect Slack or Telegram, done. There's no per-monitor cost, no seat fee, no vendor terms to reread.

The trade is that it checks from wherever you host it, and when that box has a bad day (a full disk, a kernel update, a host outage), your monitoring goes down with it and nothing tells you. For personal projects, fine. For paying clients, be honest with yourself about whether you want alerting to be a hobby-grade responsibility. If you go this route, put an external heartbeat on the Kuma instance itself so something watches the watcher.

Pick it if you have the ops habit already and the budget is zero.

Comparison table

Cost per client site

Take a 50-client agency with two monitors per site, 100 monitors total, on monthly billing.

Sentinel is second cheapest, not cheapest. The ten dollars between Notifier and Sentinel buys four-region verification on every check, all check types, and five seats. Whether that's worth 20 cents a client a month depends on how much a false alert costs you; for most agencies it's one annoyed client email, which is more than 20 cents.

Setting it up in an afternoon

Whatever you pick, the shape is the same. Here's the Sentinel version.

1. Make a group per client. Name it what you call them on the invoice.
2. Add the monitors. Homepage, the page that makes money, SSL and domain expiry. Four monitors per client covers most of what actually breaks.
3. Route the alerts. Point the group at the client's Slack channel or the account manager's Telegram, and your own on-call at the top level. Nothing goes to a shared inbox nobody watches.
4. Publish a status page per client. On their subdomain if they'll give you a CNAME, on yours if they won't.
5. Send the report. On Business, a white-label monthly uptime report goes out automatically. Attach it to the invoice and monitoring stops being invisible.

Frequently asked questions

How many monitors does a client site need? Two is the floor (homepage and SSL). Four is typical (add domain expiry and the login or checkout page). Sites with a JSON API or a cron job that matters get one more each. Budget on four per client and you'll rarely be wrong.

Can I use UptimeRobot's free plan for client sites? On paper, yes, since May 2026. In practice the free plan ran under non-commercial compliance notices for most of a year, and the fair-use policy that replaced them resolves account reviews by moving you to a paid plan. Here's the full story. Sentinel's free plan has no such history: client work is allowed, and it says so.

Should monitoring be a line item in the retainer? Yes, and price it at what it's worth rather than what it costs you. At $0.58 a site your cost is invisible; the value to the client is knowing before their customers do. A $10 to $25 monthly line item is normal, and the status page and report are what make it feel real.

Do I need 30-second checks for client sites? Usually not. A one-minute check catches an outage within a minute and re-verifies before alerting. Thirty seconds matters for checkout flows and APIs where every minute is revenue; for a marketing site it's a nicer number, not a different outcome.

Why do I get alerts when the site is fine? Because the tool checks from one place and that place had a bad route. It's the most common complaint about single-location monitors and the reason Sentinel checks from four regions and needs agreement before it pages you.

How do I offboard a client? Pause the group, keep it a month in case they come back, then delete it. On Sentinel, deleting the group removes the monitors, the status page and the routing in one step, and the seat count doesn't change because nobody's paying per seat.

Where to start

If you're a freelancer or small agency with a roster you're accountable for, start on Sentinel's free plan, put your ten most important client sites on it, and see whether the alerts you get are ones you'd have wanted. If you're already on UptimeRobot's free plan, read the fair-use policy before your next client signs. And if you'd rather self-host, run Kuma and put a heartbeat on it.

The tool matters less than the habit. Every client site monitored from more than one place, a status page they can see, and a report with your name on it. Pick whichever one lets you do that at a price you can write into the retainer.