list_runs vs get_run vs job_log vs pr_checks each target a distinct CI object/level, and failure_summary is explicitly framed as the aggregation starting point. The main soft overlap is that get_run already surfaces failed jobs/steps and job_log can surface error lines, so failure_summary is partly a convenience composite of the other two, but the guidance makes the intended selection clear.

All names are snake_case and readable, but the verb convention is mixed: list_runs and get_run are verb_noun while job_log, failure_summary, coverage, and pr_checks are bare noun phrases. A uniform scheme (e.g. get_job_log, get_coverage, get_pr_checks) would make the set more predictable.

Six tools is tightly scoped to the read-only CI-diagnostics purpose, with no obvious filler or near-duplicate entries. Each tool maps to a distinct stage of the debugging workflow: discover runs, inspect a run, drill into logs, summarize failures, check coverage, check PR status.

The read-only surface covers the core red-build triage loop well, from run listing through failure diagnosis and coverage. Gaps are minor for the stated scope: no rerun/trigger, no artifact retrieval, and no cross-run search or flaky-test history, but agents can work around these.