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Agent skill

Nekocap Runtime Cautions

by nopol10 in nopol10/nekocap

A skill your agent uses when working on Next.js routing/middleware, error handling, Sentry/logging, user-facing notifications, performance-sensitive paths (Octopus subtitle renderer, large lists…

GPL-3.0Auto-check passedMedia & Creative

Install Nekocap Runtime Cautions

skills CLI
$ npx skills add nopol10/nekocap --skill nekocap-runtime-cautions -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install nopol10/nekocap nekocap-runtime-cautions --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/nopol10/nekocap.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/nekocap-runtime-cautions .claude/skills/nekocap-runtime-cautions && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
nekocap-runtime-cautions
GitHub stars
105
Token cost
~1.4k tokens
SKILL.md length
647 words
Files
1
Skills in repo
5
Repo updated
First seen
Licence
GPL-3.0

At a glance

A skill your agent uses when working on Next.js routing/middleware, error handling, Sentry/logging, user-facing notifications, performance-sensitive paths (Octopus subtitle renderer, large lists…

  • Working on Next.js routing/middleware
  • SKILL.md covers Routing (web), Error handling, Logging and Performance hot-paths, plus 3 more sections
  • Calls npm
  • User-facing notifications

What it does

Nekocap Runtime Cautions is an agent skill from nopol10/nekocap. Use when working on Next.js routing/middleware, error handling, Sentry/logging, user-facing notifications, performance-sensitive paths (Octopus subtitle renderer, large lists, history-state debouncing, React Compiler / memoization), or any change to caption parsing or the caption editor. Also load this when verifying a change since there are no automated tests.

Its SKILL.md is about 1.4k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Media & Creative, covering Transcription and Error handling. It works with Sentry, React, Next.js and Redux. The repository describes itself as: Browser extension for creating & uploading community captions for YouTube, niconico and other video sharing sites. The licence is GPL-3.0.

When your agent uses it

  • Working on Next.js routing/middleware
  • User-facing notifications
  • Performance-sensitive paths (Octopus subtitle renderer
  • History-state debouncing

Example prompts

  • “/nekocap-runtime-cautions”

What it can do on your machine

Read from SKILL.md and the folder at commit cf47362. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Shell commands in SKILL.md call:

    • npm

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md. Its commands use npm, which can reach the network depending on how they are called.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Nekocap Runtime Cautions loads about 1.4k tokens when it runs. Until then it costs about 97 tokens; SKILL.md has 647 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~97
When it runs · the whole SKILL.md, loaded when a task matches
~1.4k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from nopol10/nekocap at commit cf47362, republished under its GPL-3.0 licence (© nopol10). 647 words, ~1,392 tokens.

Download SKILL.mdSave it as .claude/skills/nekocap-runtime-cautions/SKILL.md (or your agent's skills folder).
name
nekocap-runtime-cautions
description
Use when working on Next.js routing/middleware, error handling, Sentry/logging, user-facing notifications, performance-sensitive paths (Octopus subtitle renderer, large lists, history-state debouncing, React Compiler / memoization), or any change to caption parsing or the caption editor. Also load this when verifying a change since there are no automated tests.

This skill covers the runtime behaviors that don't fit cleanly elsewhere: routing, error handling, logging, performance hot-paths, and the project-specific gotchas that will silently bite agents who don't know about them.

Routing (web)

  • File-based under pages/. SSG with getStaticProps (often wrapped via wrapper.getStaticProps() from next-redux-wrapper) is the default; use getServerSideProps only when you genuinely need per-request data.
  • middleware.ts handles /browse → /browse/1, Firebase auth rewrites under /__/auth/*, and YouTube Shorts / watch URL → /create redirects. If you add a new URL shortcut or platform deep link, update this file.
  • react-router-dom@5 is used only inside the extension popup — don't import it in web code.

Error handling

  • User-facing notifications: use antd's message API (message.info, message.error). The content script already wires ChromeMessageType.InfoMessage → message.info(payload.message, payload.duration).
  • Saga errors: wrap with safe() from src/common/redux-utils.ts (see the nekocap-redux-feature skill). Unwrapped sagas kill the entire saga middleware silently.
  • Web errors: Sentry is configured via sentry.client.config.js / sentry.server.config.js and NEXT_PUBLIC_SENTRY_DSN.
  • Extension errors: no Sentry coverage. Anything thrown in background/, content/, popup/, or canvas-iframe/ only reaches the devtools console.
  • No global error boundary. react-error-boundary is installed but unused. If you wrap a risky tree, do it locally; don't add a global boundary without a discussion.

Logging

  • console.error / console.warn / console.log used directly — no project logger utility.
  • redux-logger is enabled in dev only (process.env.PRODUCTION ? undefined : logger in src/common/store/store.tsx). Don't enable it in production.
  • No analytics (no Mixpanel, no GA). Don't add one without a discussion.

Performance hot-paths

  • Octopus subtitle renderer is isolated in a sandboxed iframe (src/extension/content/canvas-iframe/ + src/extension/content/containers/octopus-renderer-iframe-proxy.tsx) to keep its workload off the host page's main thread. Anything you add that runs per subtitle frame must stay inside that iframe or be cheap enough to not affect playback.
  • YouTube history-state navigation is debounced 1s in src/extension/background/index.tsx (~line 257). Reducing or removing the debounce causes double-injection.
  • Lists: use rc-virtual-list or react-virtualized (both already installed) for anything over ~50 rows. Don't render thousands of subtitle entries unvirtualized.
  • Memoization: the project relies on babel-plugin-react-compiler (React Compiler RC). Don't sprinkle useMemo / useCallback defensively — the compiler handles it. Add manual memoization only with a measured reason.
Show full SKILL.md (310 more words)Show less

Project-specific cautions — these will bite you

  • NO TEST COVERAGE EXISTS. Vitest is wired up (vitest.config.ts) but the test suite is empty. npm run test passes because there's nothing to run. Manual verification in a real browser is the only safety net. After any change, load the unpacked extension on an actual video page (or run npm run watch:web for web changes), exercise the code path you touched, and watch the devtools console for errors. Don't trust "it builds" as proof of correctness.

  • Caption-editor mutations fail silently. There's a // TODO send error message to content script at src/common/feature/caption-editor/sagas.ts:304. Failed validation or parsing does not surface a toast — the user sees nothing. When touching caption editing, watch the background console; don't trust the absence of an error message.

  • Persisted Redux state can poison users. State is written to chrome.storage.local (see the nekocap-redux-feature skill). A bad shape ships to every existing user and stays there until they reset the extension. Migrations matter.

  • MV3 CSP forbids external scripts — see the nekocap-extension-messaging skill if you're adding runtime dependencies.

When you change X, also check Y

If you change…Also verify…
Caption parsing / Octopus renderingManually test ASS, SRT, and VTT — there are no tests
Caption-editor flowWatch the background console for silent mutation errors
middleware.tsThe redirect chain still works for YouTube Shorts/watch links
Performance-sensitive codeProfile in devtools; React Compiler output may not match your assumptions
Any extension changeTested in both Chrome AND Firefox unpacked builds

Anti-patterns

  • Don't add useMemo / useCallback defensively. Do trust the React Compiler unless you've measured.
  • Don't introduce a global error boundary unannounced.
  • Don't add analytics, a custom logger, or a second notification system. Use message from antd.
  • Don't rely on npm run test passing as a correctness signal — the suite is empty.
  • Don't ship a Redux state shape change without a migration plan.
  • Don't render >50 rows unvirtualized.

© nopol10, GPL-3.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/nekocap-runtime-cautions of nopol10/nekocap.

Open the folder on GitHubat commit cf47362

Compare with similar skills

Nekocap Runtime Cautions next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Nekocap Runtime Cautions compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Nekocap Runtime Cautions this skillnopol10/nekocap105—~1.4kAutomated safety check: PassGPL-3.0
Next Best Practicesvercel-labs/openreview1.7k18 repos~1kAutomated safety check: PassNone
Add Error Trackinggotempsh/temps826—~4.2kAutomated safety check: NotesApache-2.0
Sentry SDK Setupgetsentry/sentry-for-ai268—~1.7kAutomated safety check: PassApache-2.0
Remotion Best Practiceslyonjs/shortvid.io14733 repos~1kAutomated safety check: PassMIT
Dotlottie WebLottieFiles/dotlottie-web892—~3.5kAutomated safety check: PassMIT

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Works with

Categories

Questions about Nekocap Runtime Cautions

What does Nekocap Runtime Cautions do?

A skill your agent uses when working on Next.js routing/middleware, error handling, Sentry/logging, user-facing notifications, performance-sensitive paths (Octopus subtitle renderer, large lists…. Nekocap Runtime Cautions is an agent skill from nopol10/nekocap.js routing/middleware, error handling, Sentry/logging, user-facing notifications, performance-sensitive paths (Octopus subtitle renderer, large lists, history-state debouncing, React Compiler / memoization), or any change to caption parsing or the caption editor.

When should I use Nekocap Runtime Cautions?

Nekocap Runtime Cautions fits situations like: working on Next.js routing/middleware; user-facing notifications; performance-sensitive paths (Octopus subtitle renderer; history-state debouncing.

How do I install Nekocap Runtime Cautions in Claude Code?

Run `npx skills add nopol10/nekocap --skill nekocap-runtime-cautions -a claude-code`. Or copy the skill folder (.agents/skills/nekocap-runtime-cautions in nopol10/nekocap) into .claude/skills/nekocap-runtime-cautions in your project. Claude Code loads it when a task matches its description.

How do I install Nekocap Runtime Cautions in Codex?

Run `npx skills add nopol10/nekocap --skill nekocap-runtime-cautions -a codex`. Or copy the skill folder (.agents/skills/nekocap-runtime-cautions in nopol10/nekocap) into .agents/skills/nekocap-runtime-cautions in your project. Codex loads it when a task matches its description.

Can I use Nekocap Runtime Cautions in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add nopol10/nekocap --skill nekocap-runtime-cautions -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/nekocap-runtime-cautions, .gemini/skills/nekocap-runtime-cautions, .github/skills/nekocap-runtime-cautions and .opencode/skills/nekocap-runtime-cautions in your project.

What does Nekocap Runtime Cautions need to run?

Going by SKILL.md and its folder, Nekocap Runtime Cautions needs the command-line tools its instructions call (npm).

Does Nekocap Runtime Cautions access the network?

SKILL.md contains no URLs. Its commands use npm, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Nekocap Runtime Cautions safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Nekocap Runtime Cautions use?

Nekocap Runtime Cautions is published under the GPL-3.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Nekocap Runtime Cautions use?

About 1.4k tokens (SKILL.md is roughly 5.6k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Nekocap Runtime Cautions?

Skills that share tags, products or a category with Nekocap Runtime Cautions: Next Best Practices (vercel-labs/openreview, 1.7k stars), Add Error Tracking (gotempsh/temps, 826 stars), Sentry SDK Setup (getsentry/sentry-for-ai, 268 stars) and Remotion Best Practices (lyonjs/shortvid.io, 147 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Nekocap Runtime Cautions?

nopol10 (a GitHub user) maintains it in nopol10/nekocap, which has 105 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on October 3, 2026.

Source: nopol10/nekocap on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.