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.
npx skills add sidiangongyuan/codex-skills-library --skill app-feature-craftgit clone --depth 1 https://github.com/sidiangongyuan/codex-skills-libraryWrote 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.
[](https://agentmods.dev/skills/sidiangongyuan/codex-skills-library/app-feature-craft)<a href="https://agentmods.dev/skills/sidiangongyuan/codex-skills-library/app-feature-craft"><img src="https://agentmods.dev/badge/skills/sidiangongyuan/codex-skills-library/app-feature-craft/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.
<a href="https://agentmods.dev/skills/sidiangongyuan/codex-skills-library/app-feature-craft"><img src="https://agentmods.dev/badge/skills/sidiangongyuan/codex-skills-library/app-feature-craft.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00052 | $0.00867 |
| Opus 5.5 | $0.00021 | $0.00347 |
| Sonnet 5.5 | $0.00010 | $0.00173 |
| Haiku 4.5 | $0.00005 | $0.00087 |
Grade A, and why
app-feature-craft 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.
How it starts
The opening of the file, as written. The whole thing — 87 lines — stays where its author put it; the contents beside it link to each section on GitHub.
App Feature Craft
Use this skill to turn an app request into a feature users can actually rely on. Default to shipping the smallest complete behavior, not a technical stub.
Workflow
-
Ground in the product before designing.
- Inspect routes, screens, state stores, API clients, backend handlers, data models, tests, packaging scripts, and existing copy.
- Resolve discoverable facts from the repo before asking the user.
- If visual behavior matters, inspect screenshots or run the app.
-
Define the user-facing outcome.
- State what the user can do after the change.
- Identify the audience, success criteria, in/out of scope, data safety constraints, and where the behavior must appear.
- Separate optional convenience from behavior required for a complete feature.
-
Design the whole path.
- Cover UI states: empty, loading, success, failure, stale data, first-run, and already-configured.
- Keep controls near the user's task context. Avoid bolted-on panels, rigid form-heavy surfaces, or result views that disappear behind an ambiguous "back" action.
- Prefer reading-first UI with focused edit affordances for dense knowledge or writing surfaces.
- Cover data/API behavior: persistence, validation, compatibility, migration, idempotency, and failure modes.
- Cover lifecycle behavior for desktop apps: startup, restart, sidecars, installer state, and local paths when relevant.
- For long-running AI or provider work, design background progress, reopening/recovery, cancellation semantics, and honest stage labels before implementing the request.
-
Implement narrowly.
- Follow existing local patterns instead of inventing a new framework.
- Keep user data safe by default; never delete, overwrite, or migrate destructively unless the user explicitly asked for it.
- Do not expose raw backend/browser errors in public UI.
- Do not report a fake success for external integrations. Mocked tests prove code paths, not real provider availability.
- Run only the user-selected AI/profile/configuration set. Do not silently add a default provider after the user made an explicit choice.
- Keep separate provider profiles and locally saved keys isolated by owner; never let one profile's credential overwrite another profile's source.
- Make AI-generated drafts, candidate imports, and writeback actions review-first unless the user explicitly requested automatic mutation.
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 1mo ago First seen · 87 lines · 52 tokens per session scan A 80092939458f
app-feature-craft is a skill published in the GitHub repository sidiangongyuan/codex-skills-library (24 stars, last pushed 1mo ago), licensed MIT. It adds 52 tokens to every session and 867 once invoked, about $0.0002 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 2026-08-31.
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