Can it tell me which job failed?

The status read gives you the pipeline result. For the failing step, the agent follows up with get_build_failure_logs, which returns the failure logs it can summarize into the message.

Does it post on every run or only on changes?

On changes, if you track state. Have the agent remember the last status per branch and post only on a transition, so a branch that stays red doesn't repeat the same alert.

CircleCIRocket.Chat

Post CircleCI pipeline failures to a Rocket.Chat channel

A CircleCI + Rocket.Chat agent flow

Is main green right now? On most teams the honest answer is whoever last looked. This flow keeps that answer in a Rocket.Chat channel instead of in someone's memory. The agent checks the latest pipeline for a branch with get_latest_pipeline_status, and when the status comes back failed it posts to a self-hosted Rocket.Chat channel with send_message, naming the project, the branch, and linking the pipeline. CircleCI reports status on request, so the agent polls on a short loop, compares against the last status it saw, and posts only when the branch flips from passing to failing, or recovers.

The flow

CircleCIget_latest_pipeline_status

Gets the status of the latest pipeline for a branch.

Rocket.Chatsend_message

Send a message to a channel.

Step by step

Pick the branch and the channel
Tell the agent the CircleCI project slug and the branch to watch, usually main, and the Rocket.Chat channel to post into.
Check the latest pipeline
The agent calls get_latest_pipeline_status for the branch and reads whether the most recent pipeline succeeded, failed, or is still running.
Post on a state change
Hold the last status. When the branch goes from green to failed the agent calls send_message with the project, branch, and pipeline link; when it recovers, it posts an all-clear.

Tell your agent

Every two minutes, get the latest CircleCI pipeline status for acme/web on the main branch. If it changed to failed since the last check, post to the Rocket.Chat channel 'build-status' with the project, branch, and pipeline link. Post an all-clear when it goes back to passing, and stay quiet while the status is unchanged.

Setup

This flow needs both servers connected to your agent. Follow each install guide:

CircleCI install guide Rocket.Chat install guide

Worth knowing

get_latest_pipeline_status reports the latest pipeline only. If you watch several branches, the agent calls it per branch and tracks each branch's state separately.
A pipeline can be in a running state when the agent polls. Treat running as 'no change yet' rather than a failure, or the agent posts before the result is known.
send_message posts by channel name or ID depending on your Rocket.Chat setup. Confirm the bot account is a member of the channel, or the post is rejected.

Questions

Can it tell me which job failed?: The status read gives you the pipeline result. For the failing step, the agent follows up with get_build_failure_logs, which returns the failure logs it can summarize into the message.
Does it post on every run or only on changes?: On changes, if you track state. Have the agent remember the last status per branch and post only on a transition, so a branch that stays red doesn't repeat the same alert.