react-doctor

react-doctor is a skill for Claude Code, Codex from PostHog/posthog-foss. It costs 32 tokens per session (346 once invoked), scanned A, original, MIT.

A diagnostic guide for React applications that checks security, correctness, performance, architecture, accessibility, and unused code. React is a JavaScript library for building user interfaces.

In plain words
What is it for?
It is for scanning a React or Next.js project, fixing issues such as unsafe code, incorrect state handling, large bundles, missing metadata, and accessibility gaps, then running the scan again to check the result.
Why use it?
It helps locate common problems with file paths and line numbers instead of relying only on a general code review. A score and severity ordering help decide what to inspect first.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: installed under .agents/ (shared by several agents).

Good fit It is for scanning a React or Next.js project, fixing issues such as unsafe code, incorrect state handling, large bundles, missing metadata, and accessibility gaps, then running the scan again to check the result.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/posthog/posthog-foss/react-doctor
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.

Any agent
npx skills add PostHog/posthog-foss --skill react-doctor
Clone the repo
git clone --depth 1 https://github.com/PostHog/posthog-foss

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for react-doctor

README.md
[![agentmods](https://agentmods.dev/badge/skills/posthog/posthog-foss/react-doctor/github.svg)](https://agentmods.dev/skills/posthog/posthog-foss/react-doctor)
Your own site
<a href="https://agentmods.dev/skills/posthog/posthog-foss/react-doctor"><img src="https://agentmods.dev/badge/skills/posthog/posthog-foss/react-doctor/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for react-doctor

Your own site · 80×15
<a href="https://agentmods.dev/skills/posthog/posthog-foss/react-doctor"><img src="https://agentmods.dev/badge/skills/posthog/posthog-foss/react-doctor.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 346 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium MCP Rug Pull · line 14
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
How audits are shown
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 5.1 $0.00032 $0.00346
Opus 5.5 $0.00013 $0.00138
Sonnet 5.5 $0.00006 $0.00069
Haiku 4.5 $0.00003 $0.00035

Measured 1mo ago against content hash f2b529172abd, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

react-doctor scanned grade A with 0 findings 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 1mo ago.

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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/react-doctor/SKILL.md · 42 lines

What it actually says

React Doctor

Scans your React codebase for security, performance, correctness, and architecture issues. Outputs a 0-100 score with actionable diagnostics.

Usage

npx -y react-doctor@latest . --verbose

Workflow

  1. Run the command above at the project root
  2. Read every diagnostic with file paths and line numbers
  3. Fix issues starting with errors (highest severity)
  4. Re-run to verify the score improved

Rules (47+)

  • Security: hardcoded secrets in client bundle, eval()
  • State & Effects: derived state in useEffect, missing cleanup, useState from props, cascading setState
  • Architecture: components inside components, giant components, inline render functions
  • Performance: layout property animations, transition-all, large blur values
  • Correctness: array index as key, conditional rendering bugs
  • Next.js: missing metadata, client-side fetching for server data, async client components
  • Bundle Size: barrel imports, full lodash, moment.js, missing code splitting
  • Server: missing auth in server actions, blocking without after()
  • Accessibility: missing prefers-reduced-motion
  • Dead Code: unused files, exports, types

Score

  • 75+: Great
  • 50-74: Needs work
  • 0-49: Critical
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. 1mo ago First seen · 42 lines · 32 tokens per session scan A f2b529172abd

Subscribe to this mod's changes

react-doctor is a skill published in the GitHub repository PostHog/posthog-foss (726 stars, last pushed today), licensed MIT. It adds 32 tokens to every session and 346 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Related

Other skills, from other repositories

devtools-react

React adapter for the json-render devtools inspector. Use whenever the user wants to add, configure, or troubleshoot @json-render/devtools-react in a React json-render app, including spec inspection, state editing, action and stream timelines, catalog browsing, or DOM picking.

vercel-labs/json-render · 58 tokens

material-ui-nextjs

Integrates Material UI with Next.js App and Pages routers using @mui/material-nextjs, Emotion cache providers, next/font, CSS layers with Tailwind/CSS Modules, Link component prop patterns, CSS theme variables SSR notes, and App Router useSearchParams + Suspense. Use when setting up or debugging MUI in a Next.js app.

mui/material-ui · 76 tokens

migrate-oxlint

Guide for migrating a project from ESLint to Oxlint. Use when asked to migrate, convert, or switch a JavaScript/TypeScript project's linter from ESLint to Oxlint.

oxc-project/oxc · 44 tokens

inspector-workbench

Runs Inspector UI work on the standalone Threads state lab so the agent can see the overlay. Use when a CopilotKit employee asks an agent to fix, polish, add, or debug Inspector UI, chrome, panes, overlay actions, launcher, Home, Threads, Playground, Memory, or any visual behavior in @copilotkit/web-inspector. Don't…

CopilotKit/CopilotKit · 112 tokens

devtools-bidirectional

Two-way event patterns between devtools panel and application. App-to-devtools observation, devtools-to-app commands, time-travel debugging with snapshots and revert. structuredClone for snapshot safety, distinct event suffixes for observation vs commands, serializable payloads only.

TanStack/devtools · 59 tokens

devtools-instrumentation

Analyze library codebase for critical architecture and debugging points, add strategic event emissions. Identify middleware boundaries, state transitions, lifecycle hooks. Consolidate events (1 not 15), debounce high-frequency updates, DRY shared payload fields, guard emit() for production. Transparent server/client…

TanStack/devtools · 64 tokens