A nightly agent loop opened 61 PRs in a weekend; the human merged 52, because the loop is not allowed to
Peter Vanhee's adapted Ralph loop runs headless Claude Code 18:00–06:00 on an always-on laptop: GitHub issues labelled ready become one PR each, merging is denied at the permission level, a usage gate fails closed, and the morning is a review shift.
Source: The nightly Ralph loop
Peter Vanhee switched on a loop one Friday evening that turns GitHub issues into pull requests while he is away. By Sunday night it had opened 61 PRs across five repositories; he merged 52, closed one, and eight were still waiting. The loop merged none: "it isn't allowed to."
It is Geoffrey Huntley's Ralph idea — the same prompt fed to a coding agent in a loop, with continuity in files and git rather than the model's context — run as headless Claude Code (claude -p) on an always-on Linux laptop: about 340 lines of bash, two prompts, a permissions file and four systemd units. A timer starts the night at 18:00 and a second polls every 30 minutes, so a breakfast comment is picked up within the half hour. Issues labelled ready are approved work; anything else is invisible. Each gets a fresh worktree and its own branch. Before new work, the loop answers feedback on its open PRs — his comments, Copilot reviews capped at two rounds, or a conflict with main.
The safety comes from boring mechanisms. Merging, force-pushing and publishing are on a deny list, not just discouraged in a prompt. A 23-line usage gate ends the night if tonight's share of the weekly subscription limit, the week overall or the five-hour window crosses a threshold, and reports 100% if it can't read the numbers. Each issue has a 90-minute timeout and a $25 ceiling. When only he can decide — a price, a name — the agent writes one question with a recommended answer, labels it needs-decision and stops: "A clear question is a good night's work. A guess that costs a morning is not." The first real failure was the loop's own PRs colliding on shared files; the fix was less collision (additive edits, an After #N ordering line), not smarter conflict resolution.
Why it matters for code review
This is the overnight harness at personal scale, and it makes the trade explicit: "the cost of writing code has moved to reviewing it, which was the point." The next number he plans to watch is review minutes per merged PR. Pair with Crosley's Ralph loop overnight harness and the review queue as the real limit on agents.