amlint

Semantic linter for Prometheus Alertmanager configs.

Alertmanager's own amtool check-config already validates most schema-level mistakes and refuses to start over them. amlint covers that same ground in one dependency-free CLI with JSON/SARIF/diff/tree output, plus checks that amtool doesn't do — configs that load fine, that Alertmanager runs without complaint, and that still silently don't do what you meant: unreachable routes behind a catch-all, timing that contradicts itself, inhibition rules that silence too broadly.

Try it without installing anything: the playground checks a config in your browser, and the config never leaves the page.

Open the playground

Quick example

pip install amlint
amlint check alertmanager.yml

  ERROR  Route references receiver 'pager-team' which is not defined in receivers.
         Alerts matched here will be dropped.
  ↳ route.routes[1]  [undefined-receiver]

  WARN   Catch-all route (no matchers) with continue:false will intercept all alerts
         — 2 subsequent sibling(s) are unreachable.
  ↳ route.routes[0]  [unreachable-route]

  2 error · 3 warn · 1 info

Exit code 1 on any ERROR — ready for CI. --strict treats WARN as failure too.

Why not just amtool?

	amtool	amlint
Syntax errors	✅	✅
Undefined receiver	✅	✅
Missing integration fields (webhook url, PagerDuty key, etc.)	✅	✅
Bad regex in matchers	✅	✅
Unreachable routes (catch-all swallows siblings)	❌	✅
Route matcher collisions	❌	✅
Shadowed routes (an earlier, broader sibling catches every alert)	❌	✅
Inhibition rules that silence too broadly, or never fire	❌	✅
Timing misconfig (group_wait/group_interval/repeat_interval)	❌	✅
Unused or empty receivers	❌	✅
Routes and inhibit rules on alert names your Prometheus rules don't define (--rules)	❌	✅
Batch routing regression tests (label-set → expected receiver, run from a file in CI)	single alert, interactive only	✅

amtool already covers the first four rows — amlint re-implements those so you get one tool with unified JSON/SARIF/diff/tree output instead of needing the Go binary too, not because amtool misses them. Run amlint list to see exactly which of the 35 checks duplicate amtool and which don't; amlint explain <code> says so for any individual check.

On the last row: amtool config routes test already lets you test one alert's routing interactively — that part isn't new either. What it doesn't have is a way to run a whole suite of these as regression tests from a file, in CI, without a live Alertmanager. That's what amlint test adds; amlint route is the single-alert version, showing the matched routes and the group_by and timings each one inherits.

35 checks — 15 of them amtool can't do

See all checks for the full list, and which column each falls in.