Two testing skills · both proven

differential-review vs systematic-debugging

Both skills were run through Claude twice: once on a fixed brief without the skill, once with it. The briefs differ because each is written for the job the skill claims to do, so compare each skill against its own baseline, then decide which difference matters for your work.

differential-review

Performs security-focused differential review of code changes. Adapts analysis depth to codebase size, uses git blame for context, calculates blast radius by counting callers, checks test coverage of modified code, and generates a markdown report. Use when reviewing a PR, commit, or diff for security vulnerabilities, checking whether a change re-introduces a previously fixed bug, asking what else…

Category: Testing
Source: trailofbits/skills
License: Other
Proof model: claude-opus-5-5
Brief: “Do a security-focused review of this change and present it as a single HTML page. Commit: "Allow admins to impersonate users for support" +app.get('/admin/impersonate/:id', async (req, res) => { + if (req.cookies.role !== 'admin') return res.sendStatus(403); + const user = await User.findById(req.params.id); + req.session.userId = user.id; + res.redirect(req.query.next || '/'); +});”
Skill commit: 2be6433

Without the skillWith differential-review

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Without, runWith differential-review, run3 independent runs per side, none selected by hand.

Download the with-skill page

systematic-debugging

Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes

Category: Testing
Source: obra/superpowers
License: MIT
Proof model: claude-opus-5-5
Brief: “A Node.js API returns 500 for about 1 in 200 requests to POST /orders. Logs show 'TypeError: Cannot read properties of undefined (reading "id")' at orders.js:48, which reads req.user.id. The route is behind an auth middleware. The failures started after a deploy that added a 30-second cache on the session lookup. Present your diagnosis and fix as a single HTML page: what you checked, in order, the root cause, the code change, and how you would confirm it is fixed.”
Skill commit: bb92a77

Without the skillWith systematic-debugging

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Without, runWith systematic-debugging, run3 independent runs per side, none selected by hand.

Download the with-skill page

We don’t pick a winner for you: the pages are the evidence. Both proofs can be repeated with the brief, model and commit shown above. See alternatives to differential-review or alternatives to systematic-debugging.