Click, not code:
monitor client sites without writing TypeScript
Checkly is monitoring-as-code for developers: checks defined in TypeScript, deployed via CI, version-controlled in Git. If your monitoring need is "agency-shaped" - per-page Lighthouse, AI visual regression, a white-label weekly report built to forward - Checkly is the wrong shape and writing TypeScript per check is overhead you do not want. SiteLetter is built for exactly that job, at $4.80/site a month with every monitor on.
Also evaluating Better Stack, Hyperping, or Pingdom? See those comparisons, or browse all alternatives.
Quick verdict
Both tools are good at the jobs they were built for. The decision comes down to whether monitoring-as-code is your workflow or white-label client reports are your deliverable.
Developer-first engineering teams
Teams that define monitoring as code, deploy checks via CI, version them in Git, and want the checkly-cli + Terraform provider + AI-agent integration. Playwright browser checks for multi-step transaction flows. Engineering teams shipping the application and the monitoring together.
Also fits if you need private locations (self-hosted agent) or want monitoring scripted alongside application code.
Agencies sending monthly client reports
Web design, development, and marketing agencies on retainer. If what your client asks for is a recognisable Lighthouse score, evidence that nothing broke this week, and a branded weekly or monthly email rather than a code-defined check workflow, that is the job this is shaped for.
SiteLetter is priced and shaped for that job. $4.80/site a month with every monitor on covers every monitored page, and white-label scheduled reports with your logo, brand colour, agency name as sender and reply-to come with every site, at no separate rate.
Their homepage as of August 2026: "The active reliability layer for developers & agents."
"Website monitoring for agencies, delivered by email."
What the monthly client report needs beyond monitoring-as-code
Checkly ships excellent monitoring-as-code for developer teams. The things below are what the monthly client report is made of, and as of August 31, 2026 Checkly's published product and pricing documentation does not list them at any tier.
Lighthouse without a Playwright script to author
Checkly does not ship Lighthouse as a first-class product. Users currently roll their own Lighthouse runs inside a Playwright script - it has been a long-standing user request on feedback.checklyhq.com. For an agency that means writing and maintaining a JavaScript test harness per client site. SiteLetter runs Google Lighthouse on every monitored page across every client site daily, with DNS, TLS, and CDN cache warmup before each audit, and ships the Performance, Accessibility, SEO, and Best Practices scores in the weekly client report with no code to maintain.
Day-over-day diffs, not Playwright golden-image assertions
Checkly's visual regression is golden-image comparison inside a Playwright check - developer-written assertions that fail when the rendered screenshot diverges from a stored baseline. That is test-style regression, useful in CI before a deploy ships. SiteLetter ships the continuous-monitoring shape instead: a full-page screenshot of every monitored page on mobile and desktop every 24 hours, then an AI classifier across each diff big enough to matter. Rotating banners and cookie variants get dismissed as cosmetic noise; a genuine content change lands in the next scheduled client report; a real layout break is flagged in the dashboard and called out in the report you forward.
Per-site billing, not two parallel quotas
Checkly meters with two parallel quotas - uptime monitor count and browser/API check run volume - and tiers them: Hobby Free covers 10 monitors, Starter $24/mo covers 50, Team $64/mo covers 75, Enterprise above. On uptime the counts stay small either way: SiteLetter probes one page per site, the homepage, so six client sites is six Checkly monitors and sits inside Hobby Free. Uptime is not where the two tools part company. SiteLetter is $4.80/site a month with every monitor on, and Lighthouse, screenshots and broken-asset checks run daily on up to 15 pages per site, with SSL and domain expiry checked daily for the site itself and sitemap discovery re-syncing weekly. Uptime probes the homepage every minute. No quota math.
Scheduled reports for clients, not failure alerts for engineers
Checkly's email surface is alert-only: a check failed, here is the trace, here is the screenshot. There is no scheduled, per-client branded weekly or monthly report flow - no per-client logo, brand colour, or reply-to address on a scheduled artifact. SiteLetter is built around that flow end to end. The recipient opens the white-label report from their inbox with no SiteLetter login screen and no account to create.
White-label client reports, and agency client use their terms restrict
Checkly does ship white-label, on the status page: their pricing page offers to "Remove all Checkly branding from your status page for a fully branded experience", plus your own CSS. What it does not reach is an email deliverable, because there is no scheduled report to brand. Their Use Restrictions clause (Section 2.7 of checklyhq.com/terms as of May 2026) also restricts "sell, resell, encumber, rent, lease, time-share, distribute, transfer or otherwise use or make available... for the benefit of any third party", so agencies running reseller arrangements on Checkly need explicit written consent. SiteLetter's white-label reports come with every site, at no separate rate, and resale and redistribution are permitted with written permission.
URL in, monitoring up, no code to deploy
Checkly's flagship workflow is code-defined: write checks in TypeScript, version them in Git, run them via the CLI, deploy with `checkly deploy`. They also let you declare checks in their UI, but the code path is where the product's value sits. That is a feature for engineering teams. For an agency onboarding the next client, monitoring should not require a commit. Adding a site to SiteLetter is pasting one URL. The sitemap is auto-fetched, the 15 most important pages are picked, every monitor turns on, and the report template is pre-built. Alerting is defined once at agency level rather than per site, so the next site is covered by rules you already wrote, with nothing to deploy and no second definition to keep in sync.
Feature-by-feature comparison
The full picture, grouped by category. SiteLetter wins on per-page Lighthouse, visual regression, and white-label reports. Checkly wins on monitoring-as-code, Playwright browser checks, public locations, and channel breadth. Pick by what your team ships, not by feature count.
| Feature | SiteLetter | Checkly |
|---|---|---|
| Pricing model | ||
| Pricing unit | 1 site (up to 15 pages) | Uptime monitors (count) + API and browser/Playwright check runs (volume); two separate quotas |
| Every monitor on | $4.80/site a month with every monitor on (15 pages monitored); less per site if it runs fewer of them | Hobby Free $0 (10 monitors); Starter $24/mo (50 monitors); Team $64/mo (75 monitors); Enterprise custom |
| Free tier ok for client (commercial) work | 14 days on 1 site, no card | Yes for using Checkly as your own back-end tool: no commercial-use ban in their published terms as of May 2026. Reselling Checkly access to clients is separately restricted by Section 2.7 (see the next row). |
| Reseller / white-label arrangement | White-label reports come with every site at no separate rate, sent from your own domain once you verify it; using SiteLetter to serve your own clients is allowed, reselling SiteLetter itself needs written permission (Acceptable Use, our Terms) | Status-page white-label is published ("Remove all Checkly branding from your status page"); there is no scheduled report to brand, and Use Restrictions (Section 2.7 ToS) restricts resale / making service available for third parties |
| Monitoring data retention | 2 years (730 days) for Lighthouse, screenshots, asset checks and reports; raw uptime rows kept 280 days with incidents and rolling percentages; the same window applies after a balance runs out | Raw check results vary by plan (around 30 days on Starter/Team, longer on higher tiers); aggregated rollups retained long-term |
| Per-page services on a client site | ||
| Uptime checking | Homepage every 1 min from the EU, confirmed from a second region on failure; the other 14 monitored pages are reached daily by the scan, not per minute | 1 monitor per URL; HTTPS / TCP / DNS / ICMP / heartbeat |
| Google Lighthouse audits (Performance / Accessibility / SEO / Best Practices) | Every monitored page, daily, with cache warmup | No first-class Lighthouse product (long-standing user request on feedback.checklyhq.com); users roll their own inside Playwright |
| AI day-over-day visual regression with classification | Every monitored page, daily, classified | Visual Regression Testing on Team+ (CI-style screenshot vs stored baseline inside Playwright checks). Not continuous day-over-day diffing across every monitored page with AI classification. |
| Broken asset detection across pages | Every monitored page, daily | Not in product as a per-page check |
| Core Web Vitals (LCP, CLS) | Yes - LCP and CLS from the daily lab Lighthouse run | Not in product as labelled CWV metrics |
| Site-level services | ||
| SSL certificate expiry alerts | Yes | Yes (SSL/TLS expiry alerts) |
| Domain expiry alerts | Yes | No standalone domain-expiry product |
| Sitemap auto-discovery | Yes (weekly sync) | No (checks explicitly declared in UI or code) |
| Public status page | Not available | Yes (branded status pages tied to monitor results) |
| Multi-step transaction monitoring (Playwright) | No | Yes (flagship product; native Playwright runtime) |
| Monitoring as Code / CLI / Git workflow | No | Yes (checkly-cli, Terraform provider, GitHub Actions integration - the differentiator) |
| Client-facing reports | ||
| Scheduled client-facing email report | Yes (weekly, bi-weekly, monthly, quarterly) | No (email is alert-only) |
| Per-client branding (logo, color, reply-to) | Yes | No |
| Your branding on every report (org-level default) | Yes: white-label: your logo, your brand colour, your reply-to address, and your agency name as the sender, with the SiteLetter name taken off by one toggle, sent from your own domain once you verify it | No |
| Drag-and-drop report builder | Yes | No (alert-only delivery) |
| Recipients view reports without a login | Yes - the white-label report renders inside the email, and every report carries a public link that opens without an account. | Branded status pages accessible without login; no scheduled report-side delivery |
| Channels and platform | ||
| Multi-region probes | 3 regions (EU primary + US verifier + AP tiebreaker), monitoring data stored in the EU; screenshots go to OpenAI in the US under SCCs | 22 public locations + private locations (self-hosted agent) |
| Alert channels | Email, Slack | Email, SMS, Phone, Slack, Webhook, PagerDuty, OpsGenie, Incident.io, Rootly, MS Teams, Discord, Mattermost, Pushover, GitLab Alerts, Telegram |
| Public REST API + Terraform provider | Not available | Yes (both, all tiers) |
| Native mobile app | No | No public native mobile app |
Sources: checklyhq.com/pricing, monitoring-as-code, data retention, terms. Verified .
Which job are you buying for?
Comparing monitor counts flatters whoever wrote the comparison. These are the two questions that actually decide it, at 10 client sites.
For uptime alone, Checkly is a complete answer
Checkly's Hobby Free tier covers ten uptime monitors at no cost, which is exactly ten client homepages, and their Playwright browser checks are a far more powerful way to assert that a checkout still works than anything SiteLetter does.
SiteLetter can be bought that way too, since uptime is a line item you can switch on without the rest. But uptime alone is not the job this page is about, and pretending otherwise would mean pricing around a comparison you can run yourself in a minute.
Lighthouse, visual change detection, a branded report
Checkly is Monitoring-as-Code for developer teams. Lighthouse is not first-class, visual comparison ships as Playwright snapshot tests from Team up, which is a CI baseline rather than a day-over-day diff, and there is no scheduled branded per-client report. Matching the agency deliverable means writing it yourself.
10 client sites with every monitor on, covering up to 150 monitored pages. Prepaid, nothing recurring.
Checkly figures are the ones that vendor publishes, in the currency they publish them. Verified .
Where Checkly genuinely wins
Checkly is built for developer-first teams: checks written in TypeScript, versioned in Git, deployed through the same pipeline as the application, with Playwright browser checks and private locations. If that is how your team wants to work, Checkly is the better tool for it. The wins below are real.
Monitoring as Code (their flagship)
The `checkly-cli` lets you define every check in TypeScript or JavaScript, version-control it in Git, run it in CI (first-class GitHub Actions integration), and deploy with `checkly deploy`. Plus a Terraform provider and explicit AI-agent positioning in 2026 ("The active reliability layer for developers & agents." on their homepage as of August 2026). If your team is developer-first and wants monitoring defined alongside the application code, this is the genuine reason to pick Checkly.
Playwright-native browser checks
Multi-step browser monitoring scripted in Playwright (TypeScript/Node.js runtime) with full Chrome. Useful for ecommerce checkout flows, login funnels, complex user journeys. The flagship product. SiteLetter monitors pages individually but does not script multi-step browser flows.
Multi-region probes + private locations
22 public locations worldwide plus private locations via a self-hosted agent (Docker / Kubernetes) for monitoring services that are not reachable from the public internet. SiteLetter does triangulated multi-region probing too (EU primary + US verifier + AP tiebreaker) on a 1-minute homepage cadence, with every other monitored page reached once a day by the daily scan. Monitoring data is stored in the EU. Screenshots go to OpenAI in the US for visual change classification, under EU Standard Contractual Clauses. Checkly still wins on raw vantage-point count and on the private-locations capability for monitoring services not reachable from the public internet.
Mature alert channel breadth
Email, SMS, Phone, Slack, Webhook, PagerDuty, OpsGenie, Incident.io, Rootly, Microsoft Teams, Discord, Mattermost, Pushover, GitLab Alerts, Telegram. If your incident routing needs span any of these, Checkly covers them. SiteLetter has email and Slack today.
Public REST API + Terraform provider
Full public REST API across all tiers + an official Terraform provider on the registry. Programmatic management of every check, alert channel, and dashboard. SiteLetter has no public API today.
Generous free tier for developer experimentation
Hobby Free covers 10 uptime monitors, 10,000 API check runs/mo, 1,000 browser check runs/mo, with email/Slack/webhook alerts. Genuinely usable for a small developer project or a learning sandbox. SiteLetter starts you with 14 days of full monitoring on one site, then you buy credits.
When to pick which
Two honest scenarios.
Agencies sending client reports
Web design, development, and marketing agencies who want Lighthouse on every monitored page, AI day-over-day visual regression, and a white-label weekly report built to forward. $4.80/site a month with every monitor on, no monitoring code to write, no CI to wire.
Developer team writing monitoring-as-code
Engineering team that wants checks defined in TypeScript, deployed via CI, with Playwright browser checks for multi-step user journeys. Checkly is purpose-built for this; SiteLetter does not ship monitoring-as-code.
SiteLetter vs Checkly: FAQ
Not as a first-class native product. Lighthouse access from inside Checkly browser checks is a long-standing user request tracked on their public feedback portal at feedback.checklyhq.com, and users currently roll their own Lighthouse runs inside a Playwright script. SiteLetter runs full Google Lighthouse on every monitored page on every site daily with DNS/TLS/CDN cache warmup, and the four-score breakdown (Performance / Accessibility / SEO / Best Practices) ships in the weekly client report.
Checkly ships Visual Regression Testing as a labeled feature on Team and Enterprise tiers - automatic screenshot capture and comparison against a stored baseline inside Playwright browser checks. That is CI/test-style visual regression: the screenshot is compared against the baseline you set, the check fails if they differ, you update the baseline manually. SiteLetter is continuous: every monitored page is screenshotted every 24 hours and diffed against the last good capture, normally the previous day's, and AI classifies each diff big enough to matter as noise (rotating banners auto-dismissed), intentional update (logged in the weekly report), or real breakage (missing images, layout collapse, flagged in the dashboard and called out in the report you forward). Different shapes of the same idea - Checkly is "did the page differ from my baseline this CI run," SiteLetter is "what changed on every monitored page since it last looked right, and is any of it real breakage."
No. Checkly's email is alert-only: notifications when a check fails. There is no scheduled, per-client branded weekly or monthly report builder. SiteLetter is built around that flow.
You can consume Checkly as an end-user for your own client monitoring work, but read the Use Restrictions in their terms carefully (Section 2.7 of checklyhq.com/terms, re-read August 2026): it prohibits "sell, resell, encumber, rent, lease, time-share, distribute, transfer or otherwise use or exploit or make available any of the Service to or for the benefit of any third party". Agencies running resale arrangements (selling Checkly access to clients under your agency brand) would need explicit written agreement from Checkly. Agencies using Checkly as a back-end monitoring tool to inform their own work for clients are normal end-users. SiteLetter's terms also require written permission to resell or redistribute the Service, but using SiteLetter as an agency to monitor client sites is the intended use and is not restricted. This is not legal advice; read both sets of terms.
Monitoring as Code: Checkly's flagship workflow. The checkly-cli lets you define checks in TypeScript/JavaScript, version them in Git, run them in CI (GitHub Actions has a first-class integration), and deploy via checkly deploy. They have a Terraform provider, a public REST API, and explicit AI-agent positioning in 2026 ("The active reliability layer for developers & agents." on their homepage as of August 2026). If your team is developer-first and wants monitoring defined as code alongside the application, Checkly is the better tool today. SiteLetter does not ship monitoring-as-code, CLI, or Terraform provider.
Per-page Google Lighthouse on every monitored page daily with DNS/TLS/CDN cache warmup (Checkly has no first-class Lighthouse product). AI day-over-day visual regression that classifies each diff big enough to matter as noise / intentional / breakage (Checkly has snapshot/golden-image comparison inside Playwright scripts, not continuous classified diffing). White-label scheduled per-client email reports with per-client logo, brand color, reply-to (Checkly's email is alert-only). Sitemap auto-discovery: add a domain, SiteLetter picks the 15 most important pages and every monitor turns on for them (Checkly is per-monitor manual definition). Report branding comes with every site, at no separate rate: your logo, your brand color, your agency name as the sender display name, and your reply-to address. $4.80/site a month with every monitor on, for up to 15 pages.
It depends on which of two questions you are asking. If uptime is all you want, Checkly's Hobby Free tier covers 10 monitors at $0/mo and beats SiteLetter outright at that scale. If you want Lighthouse on every monitored page, day-over-day visual change detection and a branded client report, Checkly does not ship those, so there is no Checkly plan to compare against. SiteLetter at 10 client sites with every monitor on is $48.00/month, and that covers Lighthouse on up to 150 monitored pages.
SiteLetter keeps 2 years (730 days) of Lighthouse scans, screenshots, asset checks and reports, the same window on every account. Raw uptime check rows roll off after 280 days; uptime incidents are kept with the rest of the history. Checkly's raw retention varies by plan (around 30 days on Starter/Team, longer on higher tiers per checklyhq.com/docs/monitoring/how-we-store-data); aggregated rollups are retained long-term. For agencies showing month-over-month or year-over-year client trends from raw monitoring data, SiteLetter's 2-year retention is meaningfully longer.
Yes, with a caveat: if your existing setup depends on monitoring-as-code workflows (checks defined in TypeScript, deployed via CI, version-controlled in Git), SiteLetter does not replicate that workflow. You add sites in the SiteLetter dashboard, the product auto-discovers up to 15 pages of each site from your sitemap, falling back to the homepage's links. Lighthouse, screenshots and asset checks run on the first scan, which is booked for the next free quarter-hour, usually within minutes, and the certificate and domain expiry are read on that same scan. Uptime watches the homepage every minute. Alert rules are the one thing you write yourself: you do it once at agency level, and every client and every site inherits them. For agencies whose value is in the client deliverable (Lighthouse, visual regression, branded reports), the SiteLetter setup is shorter, and signup comes with 14 days of credits for one site so you can validate the experience before extending.
Still have questions? Get in touch.
Comparison based on publicly available Checkly pricing, terms, and feature documentation, last verified . Checkly is a trademark of its respective owner, used here for identification and comparison purposes only. SiteLetter is independent and not affiliated with, sponsored by, or endorsed by Checkly. For the most current Checkly pricing and feature information, see checklyhq.com.
You set up care-plan reporting once.
After that it runs without you.
SiteLetter is the kind of tool you forget you're using, until your client thanks you for the report you didn't write.
- ✓ Just add a domain. SiteLetter auto-discovers pages, starts monitoring, schedules reports. You pick your alert rules and who gets each report.
- ✓ No scripts to install. SiteLetter monitors from the outside, like a real visitor.
- ✓ Nothing recurring. No subscription, no contract. You buy credits when you want them and each site spends its own.