Testing vs Frontend · both proven

tdd vs vercel-react-best-practices

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.

tdd

Test-driven development. Use when the user wants to build features or fix bugs test-first, mentions "red-green-refactor", or wants integration tests.

Category: Testing
Source: mattpocock/skills
License: MIT
Proof model: claude-opus-5-5
Brief: “Implement a function that parses a cron expression (the standard five fields) and returns the next run time after a given date, in TypeScript. Present the work as a single HTML page with two columns: the test file on the left and the implementation on the right, each in a code block, with a short note at the top on the order you did things in and anything you decided not to support.”
Skill commit: 5beb35b

Without the skillWith tdd

⇆

Without, runWith tdd, run3 independent runs per side, none selected by hand.

Download the with-skill page

vercel-react-best-practices

React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.

Category: Frontend
Source: vercel-labs/agent-skills
License: Not stated
Proof model: claude-opus-5-5
Brief: “Here is a slow Next.js product list page. It fetches products, reviews and inventory one after another in a client component with useEffect, renders 500 product cards at once, imports the full lodash library, and re-sorts the list on every render. Rewrite it following current React and Next.js performance practice, and present the result as a single HTML page that shows the new code, explains each change, and estimates the impact of each.”
Skill commit: 063bee9

Without the skillWith vercel-react-best-practices

⇆

Without, runWith vercel-react-best-practices, 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 tdd or alternatives to vercel-react-best-practices.