next-dev-loop

A verification workflow for Next.js changes in a running development app. It checks both Next.js's own view of the app and what a real browser sees.

In plain words
What is it for?
Use it after editing Next.js app code to confirm the change works in the browser and matches Next.js's runtime information.
Why use it?
It catches problems that compilation and type checks can miss, such as broken routes, browser errors, or incorrect runtime behavior.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/vercel/next.js/next-dev-loop
Any agent
npx skills add vercel/next.js --skill next-dev-loop
Clone the repo
git clone --depth 1 https://github.com/vercel/next.js

Made for: Claude Code, Codex.

Per session 68 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,965 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00068 $0.01965
Opus 5 $0.00034 $0.00983
Sonnet 5 $0.00014 $0.00393
Haiku 4.5 $0.00007 $0.00197

Measured yesterday against content hash 6b8749833d92, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

next-dev-loop scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

again. Don't fall back to `curl`; it bypasses the browser you're
Origin

Copies of this mod

2 near-identical copies found in the catalogue:

skills/next-dev-loop/SKILL.md · 184 lines

How it starts

The opening of the file, as written. The whole thing — 184 lines — stays where its author put it; the contents beside it link to each section on GitHub.

next-dev-loop

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.

requires

  • Next.js 16.3+ with Turbopack/_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.

preflight

Once per session, confirm both views are live.

  1. Open agent-browser at the target URL, restoring saved login state when present. First derive one stable session id for this checkout and use it for every agent-browser command:

    SESSION="$(agent-browser session id --scope worktree --prefix next-dev-loop)"
    export AGENT_BROWSER_SESSION="$SESSION"
    export AGENT_BROWSER_RESTORE="$SESSION"
    

Read the full file on GitHub · 184 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 184 lines · 68 tokens per session scan A 6b8749833d92

Subscribe to this mod's changes

next-dev-loop is a skill published in the GitHub repository vercel/next.js (142,020 stars, last pushed yesterday), licensed MIT. It adds 68 tokens to every session and 1,965 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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