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Get Started Free →vercel/next-dev-loop
Verify Next.js runtime behavior after editing app code.
Passed 12 of 16 test cases with the skill, and 6 of 16 without it.
and 14 more in the full report
10 fixed6 passed either way4 still failing2 broke
Tokens, turns and time describe resource use, not a dollar price.
This benchmark measured an earlier version of the skill.
A newer attempt on gemini-3.6-flash on 10/2/2026 did not produce a publishable comparison (not comparable). The snapshot above is the previously measured run.
One of 9 test cases the skill fixed. Same model, same prompt, with and without the skill.
The Next.js development server output shows `Ready in 1.2s` on `http://localhost:3005`. Which environment variable must be exported before making MCP tool calls?
| Checked | Without skill | With skill |
|---|---|---|
| Sets NEXT_MCP_URL to http://localhost:3005/_next/mcp. | Missed | Passed |
The instructions your model reads when the skill loads.
The edit/verify rhythm during next dev — make a change, then
confirm it actually works at runtime, not only that the types or
the build are happy.
You verify through two views of the same running app:
/_next/mcp — an HTTP endpoint Next.js exposes about itself.
Knows framework-specific things: routes, segments, RSC, server
actions, server logs, and errors as Next.js saw them. Call
tools/list for the current surface.agent-browser — a CLI that drives a real Chrome. Knows
framework-agnostic browser things: DOM, console, network, React
fiber, vitals. Before driving it, run agent-browser skills get core
once for the version-matched usage guide — don't guess subcommands
from memory.The two views cross-check each other.
/_next/mcp plus the
proactive compile check via get_compilation_issues.agent-browser >= 0.31.1 — React introspection, worktree-scoped
session id, idempotent --restore, and launch flag reconciliation.These are hard floors, not soft preferences. If anything is missing, tell the user how to upgrade and stop. Don't fall back to grepping source or to a weaker probe — this skill assumes both views are live at the versions above.
pnpm next upgrade (or npx next upgrade).
Docs: https://nextjs.org/docs/app/getting-started/upgrading
(version-16 guide:
https://nextjs.org/docs/app/guides/upgrading/version-16)agent-browser: npm i -g agent-browser@latest.
If the CLI isn't on PATH, install it before continuing — preflight
expects to invoke it directly.test cases passed, vs 6 / 16 without
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