Response Validation

API Monitoring Beyond the 200 OK

Send custom requests to your REST APIs and health-check endpoints, then assert on the JSON response—so you catch broken APIs that plain uptime checks call healthy.

API Monitoring

3/10 assertions

GEThttps://api.example.com/v1/health

200 OK— but is the body correct?

Configured Assertions

data.statusequals"ok"

Passing

data.regionexists

Passing

data.queue.depthless than1000

Passing

Why API Monitoring?

A 200 OK doesn't mean it works

An API can return a perfect HTTP status while the response body is wrong—an error flag, a missing field, an empty list, a stale value. API monitoring validates the data itself, so contract breaks surface the moment they happen.

Verify REST API and health-check responses by field and value
Catch silent failures behind a healthy HTTP status
Monitor authenticated and write endpoints with custom requests

Assertions per Monitor

Match Operators

HTTP Methods

Global Regions

Features

Validate every response that matters

JSON Path Assertions

Target any field with dot notation—data.status, users.0.id—and assert on its exact value, not just the HTTP status.

12 Match Operators

equals, contains, exists, greater/less than, regex and their negations—validate any response contract you depend on.

Custom Requests

Send GET, POST, PUT, PATCH, DELETE, HEAD or OPTIONS with custom headers and a request body. Monitor authenticated and write endpoints.

Silent-Failure Detection

A 200 OK with the wrong data still fails the check. Catch broken APIs that plain uptime checks call healthy.

Multi-Region Checks

Assertions run from four global regions with consensus, so a real API break is confirmed everywhere before you're alerted.

Incident-Grade Alerts

A failed assertion raises a JSON assertion incident with the exact path, expected and actual value—via email, SMS, Slack or webhooks.

FAQ

API monitoring questions

What is API monitoring?

API monitoring continuously sends requests to an API endpoint and verifies the response is actually correct—not just that it returned a 200. Sentinel checks the JSON response body for the exact values your application depends on.

How does Sentinel validate a JSON response?

You add assertions, each targeting a field by dot-notation path (for example data.status) with an operator such as equals, contains, exists, greater than or regex. On every check Sentinel evaluates each assertion against the response body, and if any assertion fails the monitor is marked offline.

Can it send POST requests with a request body?

Yes. Each monitor can use GET, POST, PUT, PATCH, DELETE, HEAD or OPTIONS, with custom request headers and a request body, so you can monitor authenticated endpoints and write operations, not just public GET endpoints.

How is API monitoring different from keyword monitoring?

Keyword monitoring searches HTML pages for visible text. API monitoring validates structured JSON responses by path and value. The two check types are mutually exclusive on a single monitor because a response is either a web page or an API payload, not both.

What happens when an assertion fails?

Sentinel marks the monitor offline and opens an incident tagged as a JSON assertion failure, recording the failing path, the expected value and the actual value. You're alerted instantly via email, SMS, Slack or webhooks.

How many assertions can I add per monitor?

Up to 10 assertions per monitor, each with its own path, operator and expected value. Paths can be up to 500 characters, so even deeply nested response fields are reachable.

Go beyond uptime checks

Know your APIs return the right data

Add API monitoring and catch contract breaks before they reach your clients. 14-day free trial, cancel anytime.

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