Reviewing Buildkite CI logs

Agent Skill metadata

name: buildkite-logs
description: Fetch and inspect Julia Buildkite CI logs without web sign-in. Use when debugging Julia CI failures, reviewing Buildkite jobs, or when the Buildkite MCP is unavailable.

Use this when investigating Julia Buildkite CI failures, especially if the Buildkite MCP is unavailable. The recipe requires gh, curl, python3, and network access to GitHub and Buildkite.

Julia's CI runs on Buildkite. PR builds run in the julialang/julia-pr pipeline, post-merge master builds in julialang/julia-ci, and scheduled runs in julialang/julia-master-scheduled (the old julia-master pipeline no longer exists). The public web UI requires sign-in to download raw_log, but two frontend JSON endpoints are anonymously accessible for public pipelines. Recipe:

Find the build number. gh pr checks <PR-number> gives launcher-job URLs like https://buildkite.com/julialang/julia-pr/builds/<BUILD>#<uuid>; for a master commit, use the commit statuses (gh api repos/JuliaLang/julia/commits/<sha>/status). The #<uuid> fragments there are only the top-level launcher jobs (Build/Check/Test/…), not the per-platform jobs.
List all jobs in the build, with names, states, exit statuses, and UUIDs:
```
curl -sS -H "Accept: application/json" \
  "https://buildkite.com/julialang/<PIPELINE>/builds/<BUILD>/data/jobs" \
  -o /tmp/bkjobs.json
python3 -c "import json; [print(j['state'],'|',j.get('exit_status'),'|',j['name'],'|',j['id']) \
for j in json.load(open('/tmp/bkjobs.json'))['records']]"
```
This /data/jobs endpoint is what the build page's frontend uses; it returns every job in one page (records, plus has_next_page). Do NOT use builds/<BUILD>.json for job discovery — anonymously it returns build metadata with an empty jobs array (the statistics field still shows the true job count).
Fetch a job's log JSON (replace <PIPELINE>, <BUILD>, <JOB-UUID>):
```
curl -sS -H "Accept: application/json" \
  "https://buildkite.com/organizations/julialang/pipelines/<PIPELINE>/builds/<BUILD>/jobs/<JOB-UUID>/log" \
  -o /tmp/bk.json
```
The log text lives under the JSON output field, with embedded HTML (<time> timestamps, ANSI-as-<span> colour) and entity-encoded shell output. Strip with e.g.:
```
python3 -c "import json,re,html; s=json.load(open('/tmp/bk.json'))['output']; \
s=re.sub(r'<[^>]+>','',s); print(html.unescape(s))" > /tmp/bk.txt
```
Write the stripped log to a file and search it (logs can be hundreds of KB); piping the whole thing into context wastes tokens.

The log endpoint also serves still-running jobs (partial output). For a test job that hung, the in-tree watchdog (.buildkite/utilities/timeout.jl, JL_TERM_TIMEOUT) prints per-task Julia backtraces of every worker before killing it, and core dumps are uploaded as artifacts with an lldb bt all summary in the log — search the log for ---- Task, Waiting for, and core dumped.