API Monitoring: Because a 200 Isn't the Same as Correct
Your API can return HTTP 200 and still be wrong — a health field flipped to "degraded", a queue backing up, a total that dropped to zero. WatchFor's API monitor makes the real request, asserts on the JSON fields, headers and body text, and turns numbers from the response into charts you can alert on — each on its own scale. Status, latency and SSL are alert rules too, and you build the whole thing live with Run & inspect. It's a full HTTP monitor — SSL, timing breakdown, redirects, auth — with a response-validation engine on top.
Monitoring That Reads the Response, Not Just the Status
Everything an HTTP monitor does — plus assertions and value extraction on the body
JSON Assertions (JSONPath)
Assert on any field in the response body with JSONPath — data.status equals "ok", data.items.# is 3, data.healthy is true. Eleven operators including numeric comparisons, contains, exists and regex. Paste Checkly-style $.path or use plain dot syntax.
Extract & Chart Response Values
Pull a number out of the JSON — queue_depth, active_users, price — and it becomes a metric: charted over time and alertable on a threshold. Not a pass/fail. Watch a value trend, and get paged before it hits the wall.
Status, Latency & SSL as Alert Rules
Status code (a friendly 2xx/3xx picker), response time and certificate expiry are evaluated on the Alerting tab — so a wrong status, a slow response and a failed content assertion each raise their own descriptive incident, never a generic one.
Full SSL Certificate Monitoring
Every HTTPS check records the certificate: days until expiry, issuer and TLS version. Alert when the cert is nearing expiry — one monitor covers both the API's correctness and its certificate.
Timing Breakdown
DNS, connect, TLS handshake and time-to-first-byte are timed separately, so a slow database is instantly distinguishable from a slow network path or a cold start.
Any Method, Body & Auth
GET/POST/PUT/PATCH/DELETE with custom headers and a request body. Basic, digest or bearer-token auth, stored encrypted. HTTP/3 and legacy-TLS endpoints handled automatically.
Every Assertion, Individually
The detail page shows each assertion pass or fail with expected vs. actual — so when a check goes red you see exactly which rule broke and what the API returned, not a generic failure.
Confirmed, Multi-Region Alerts
Checks run from multiple regions with confirmation before alerting — one flaky path won't page you. Email, Slack, Discord, PagerDuty and 20+ channels.
Why 'Is It Up?' Isn't Enough for an API
An API is a contract, not a web page. The endpoint answering 200 tells you the process is running — not that the response is correct, the data is fresh, or the numbers are sane. Real API failures hide inside a successful response: a payment gateway returning {"status":"degraded"}, an inventory count silently at zero, a paginated list that lost its items, an auth token endpoint returning an empty body. A plain uptime check is blind to all of it. Reading and asserting on the response — and trending the numbers inside it — is the only way to know your API is actually doing its job.
Catch 'HTTP 200 but wrong' — the failure uptime checks can't see
Assert on JSON fields, headers and body text; status, latency and SSL as alert rules
Turn a response value into a chartable, alertable time-series
See exactly which assertion failed, with expected vs. actual
SSL certificate expiry watched on the same monitor
Full timing breakdown isolates slow DB from slow network
Counts as a regular monitor on every plan — Free included
How API Monitoring Works
Make the request, read the response, assert on what matters
Point It at Your Endpoint
Add the URL, pick the method, and set headers, a request body and auth if needed (basic, digest or bearer).
Run It and Click to Build
Hit Run request to fire the call from a real probe, see the live response, and click any field to extract it as a chartable metric or assert on it — no typing JSONPaths. Content assertions (JSON body, headers, body text) raise the Assertions Failed alert.
Extract the Numbers You Care About
Point a JSONPath at a value — data.active_users — give it a name, and WatchFor charts it over time (each value on its own scale) and lets you alert on a threshold.
Get Paged When the Contract Breaks
A failed assertion, a slow response, an expiring certificate or an extracted value crossing a threshold each alert separately — confirmed across regions, with the exact assertion that failed.
Who Monitors Their APIs This Way
If something depends on the response, assert on it
Teams Shipping Public or Internal APIs
Your API is the product for the services that call it. A malformed response or a flipped status field is a customer-facing outage even when the endpoint answers 200 — assertions catch it in minutes.
Platform & SRE Teams
Health endpoints that return {"status":"..."} are only useful if something reads them. Assert on the status field, extract the queue depth and error rate, and chart them — an early-warning system, not just a heartbeat.
Teams Watching Third-Party APIs
Payment gateways, data providers and partner APIs fail in ways their status pages don't show. Assert on the fields you actually depend on and know before your users do.
Anyone Tracking a Number Over Time
A public metric, an exchange rate, a stock level, a rate-limit remaining — extract it from the response and WatchFor turns your API into a time-series you can chart and threshold-alert.
Frequently Asked Questions
Everything you need to know about API monitoring
From our blog
Guides, deep-dives, and best practices from the WatchFor team
API monitoring beyond status codes: assert on the response, chart what matters
API Monitoring Guide: how to watch the endpoints your business runs on
HTTP Status Codes Explained: what 404, 500 and 503 really mean
Know When Your API Is Wrong, Not Just Down
Point WatchFor at your endpoint, describe what a correct response looks like, and get paged the moment the contract breaks — a failed assertion, a slow response, or a number crossing a threshold. Start free, no credit card required.