Testing vs Frontend · both proven

differential-review vs vercel-react-native-skills

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. They are in different categories, so this is a choice of job, not a head-to-head on the same job.

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

vercel-react-native-skills

React Native and Expo best practices for building performant mobile apps. Use when building React Native components, optimizing list performance, implementing animations, or working with native modules. Triggers on tasks involving React Native, Expo, mobile performance, or native platform APIs.

Category: Frontend
Source: vercel-labs/agent-skills
License: Not stated
Proof model: claude-opus-5-5
Brief: “Review and improve this React Native screen, and present the findings and the improved code as a single HTML page. ```jsx export default function Feed() { const [posts, setPosts] = useState([]); useEffect(() => { fetch(API + '/posts').then(r => r.json()).then(setPosts); }); return ( <ScrollView> {posts.map(p => ( <View> <Image source={{ uri: p.image }} style={{ width: '100%', height: 300 }} /> <Text onPress={() => navigation.navigate('Post', { post: p })}>{p.title}</Text> </View> ))} </ScrollView> ); } ```”
Skill commit: 1a2c79d

Without the skillWith vercel-react-native-skills

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Without, runWith vercel-react-native-skills, 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 vercel-react-native-skills.