API & MCP testing

API & MCP testing is Fixter’s synthetic monitoring: scheduled probes that call your endpoints from the outside, assert on what comes back, and track uptime and latency over time. HTTP APIs are one kind of target; MCP servers are the other, probed the way an agent would call them. If you ship an MCP server, this is how you find out it is broken before your users’ agents do. Tests live in the app under API Tests, and everything here is also available through the API test MCP tools, so an agent can create and inspect tests for you.

Two kinds of probes

• HTTP tests call a URL with the method, headers, and body you configure, then assert on the response: status (exact or wildcard patterns like 2xx), maximum latency, header values, and body validation in tiers from “is valid JSON” through “matches this shape” to “matches exactly”.
• MCP tests probe an MCP server the way an agent would: assert that the handshake succeeds, that tools/list returns the tools you expect, or that a specific tool call returns a valid result. If you ship an MCP server to your own customers, this is uptime monitoring for it. Both kinds are separate from alerts, which watch the telemetry your services send rather than probing them from outside.

How a test runs

Each test has an interval (down to every 30 seconds), a timeout, retries, and a failure threshold: how many consecutive failures flip it from UP to DOWN. Pausing a test parks it at PAUSED without deleting its history. Every run is recorded with its outcome and timing; the test’s page charts latency over time and computes uptime as the share of successful runs in the window you’re looking at.

Authenticating probes

Tests that call protected endpoints use stored credentials (basic auth, bearer token, API key, or OAuth2 client credentials). Credential values are write-only: once saved they are used by probes but never displayed again, and they’re managed alongside the tests themselves (or via the *_api_test_credential MCP tools).

Current limitation

API test state changes don’t send notifications yet: check status on the API Tests page or query it over MCP (get_api_test_runs, get_uptime).

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