Gage scans Claude Code sessions for bugs the diff hides

On September 4, a developer posted Gage to Show HN. It reviews the Claude Code session transcript, the conversation that produced a commit, where most review tools look only at the diff. The case behind it is simple. Claude flagged a risk mid-session, the author “didn’t read carefully, said ‘go ahead’”, and a feature broke. “Nothing in the commit shows this. It’s obvious in the session,” he wrote.

The tool is an open source CLI and TUI written in Rust and published under Apache 2 on GitHub. The author’s argument is that sessions “contain the code and the reasoning behind it”, so they give a reviewer more to work with than the diff does. Claude’s warnings and its reasons for a change stay in the transcript, and none of that reaches the commit history.

Gage reads the session files Claude Code already writes for every session under ~/.claude/projects/. The project docs describe the scans as a set of scanners: small programs that each look for one kind of issue and suggest how to resolve it. gage session list lists your sessions. gage session view shows the low-level data for each session entry, which the docs say is what the scanners see. If you leave out the session ID, it gives you a list to pick from.

Each issue Gage files has to cite lines in the session record, so every claim points back to the exchange it came from. From there you can review an issue, fix it, or close it as skipped. Gage also works with Claude Code, which can review and resolve an issue straight from the transcript.

Scans run under your own Claude login. On a subscription they count against your plan limits. On usage-based billing the author puts the cost at about $0.50 to $1.00 per scanned session. He runs Gage daily and says he pays roughly $2 for each issue resolved. At those rates, a resolved issue takes something like two to four session scans. Both figures are his own approximations.

The bug that prompted the post turned up the day before he published it, and Gage found it in a change he had approved himself. As for the rest of what it flags: “Some are minor. Some are not.”