Important news regarding Development APIs

Dear Checkmk community, especially the coding fans among you,

on the Checkmk conference, we shared that we will be building new development APIs for some important areas, where there are currently no formal APIs. See also [Nov 2023] Checkmk 2.3 roadmap update

We recently shared updates on this on the Checkmk Partner Day and feedback was that we should also share further information here. This is an initial post, and I plan to add further info here once relevant.

What APIs are we talking about:

We are building these new APIs based on an analysis of all MKPs on the Checkmk Exchange.
Consequence: if you are doing something, which is not in there, we don’t know about this. Therefore, YOU definitely need to test the APIs early on.

Why will you benefit from these APIs?

:hammer_and_wrench: Rulespec API


  • Rulesets in special agents, active checks, for check plug-ins, HW/SW inventory plug-ins.
  • Maybe: Rulesets in notification plug-ins, host monitoring rules

You are affected, if you have … created a ruleset:

grep -Rl "rulespec_registry.register" ~/local 

(from within a site)

Example: checkmk/cmk/plugins/prism/rulesets/ at master · Checkmk/checkmk · GitHub

Status: Looking good. We have migrated a couple of simple rulesets already. There is still some work to do in the API.

:hammer_and_wrench: Server-side calls API


  • Special agents
  • Active checks

You are affected, if you have created one of:

grep -e 'active_check_info' -e 'special_agent_info' ~/local/share/check_mk/checks/*

(from within a site)

This is what it impacts.

Example: checkmk/cmk/plugins/elasticsearch/server_side_calls at master · Checkmk/checkmk · GitHub

Status: Looking very good. We already migrated a lot of our own code succesfully.

:hammer_and_wrench: Graphing API

  • Metric definitions
  • Graph definitions
  • Perf-O-Meter definitions

You are affected, if you have created one of:

grep -e 'metric_info' -e 'graph_info' -e 'perfometer_info' ~/local/share/check_mk/web/plugins/metrics

(from within a site)

Currently in progress. Will add further info later here for this

New file locations!
My favorite change is this though, this however might still be subject to change. I can find now all plugins and the corresponding rulesets and checks in one place: checkmk/cmk/plugins at master · Checkmk/checkmk · GitHub
This is also where you can find all plug-ins which we already migrated!

Where is the API documentation?
You can find this inside a 2.3.0 site. For this please use a daily build. You can find them in the download archive for Checkmk daily builds. Keep in mind that the 2.3.0 daily builds are not stable. This is our development branch!
Go in the Checkmk site to “Help → Check plugin API reference”. Then you will find the current state of the API documentation.

Our migration plan:

  • Rulesets and Metrics
    • Migrate a couple of simple and complex ones to cover all functionality
      • Won’t migrate all manually, not feasible
      • Migration of all will only be done, if it is scriptable. Then we will share the script.
  • Special agents and active checks: Migrate all

Your To-Dos:

  • Use Checkmk 2.3 to migrate all extensions to APIs
    • Must for Special Agents and active checks API as current methods will be removed in 2.4
    • Will (likely) save you any worries when upgrading to 2.4
    • Effort is reasonable as not a fundamental change as with agent-based API (for check plug-ins)
  • If you can, migrate even before and let us know, if APIs are sufficient
  • We only know our code and MKPs on

We are happy to also receive your feedback in this thread!
I will also update this thread based on feedback, new learnings and so.
Of course for Checkmk 2.3, we plan to provide more resources as well. This is basically a early hint into it.

This werk describes the new APIs comprehensively: New APIs for plugin development


You mean it’s now possible to pip install cmk and start the development ? :upside_down_face: :face_with_peeking_eye: :wink:

That is what is intended in the end, if i understood our meeting at the PartnerDay correctly.
If it could be done with pip directly from pypi or from a file is another topic i think.

The idea is that you only need the packages cmk-graphing , cmk-rulesets , cmk-server-side-calls and cmk-agent-based in the future for developing monitoring plug-ins.
However, we can not promise yet that this will work.


The API development is coming to a finish soon.
Please check out the location of migrated plugins to see how stuff now looks like.

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A post was split to a new topic: Issues with apcaccess

The werk describing the changes has now been released:

We are planning a community call / developer hour as well to ask questions during the 2.3 beta phase. More details will follow.