feature-developer

feature-developer is a skill for Claude Code, Codex from henryh/AI-SpecDoc. It costs 47 tokens per session (634 once invoked), scanned A, original, MIT.

A workflow for implementing new features or major code changes as a senior developer would. It first uses the project's own documentation and conventions to guide the work.

In plain words
What is it for?
Use it when adding a significant feature or changing substantial code in a TypeScript project, including planning the implementation, handling edge cases, and checking the result.
Why use it?
It reduces the risk of code that ignores existing patterns, breaks compatibility, or misses error handling and other basic quality checks.

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/henryh/ai-specdoc/feature-developer
Any agent
npx skills add henryh/AI-SpecDoc --skill feature-developer
Clone the repo
git clone --depth 1 https://github.com/henryh/AI-SpecDoc

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 feature-developer

README.md
[![agentmods](https://agentmods.dev/badge/skills/henryh/ai-specdoc/feature-developer.svg)](https://agentmods.dev/skills/henryh/ai-specdoc/feature-developer)
Your own site
<a href="https://agentmods.dev/skills/henryh/ai-specdoc/feature-developer"><img src="https://agentmods.dev/badge/skills/henryh/ai-specdoc/feature-developer.svg" alt="Measured on agentmods" height="20"></a>
Per session 47 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 634 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. 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 $0.00047 $0.00634
Opus 5 $0.00023 $0.00317
Sonnet 5 $0.00009 $0.00127
Haiku 4.5 $0.00005 $0.00063

Measured 3d ago against content hash 2c8b91b98015, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

feature-developer 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 3d 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.

skills/feature-developer/SKILL.md · 49 lines

How it starts

The opening of the file, as written. The whole thing — 49 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Feature Developer

You are the senior developer subagent. Use this skill whenever a task involves implementing a new feature or substantial code changes.

Primary Guidance

  • Follow project conventions listed in docs/index.md.
  • Use strict TypeScript and clear modular decomposition.
  • Prefer proven, modern approaches with minimal risk and clear maintainability.
  • Prefer path aliases for commonly used project roots (e.g., src/lib, site.config.ts) to reduce deep relative imports and improve readability.
  • Keep changes scoped to the feature and update docs when needed.
  • Implement exactly to the stated requirements/acceptance criteria; clarify assumptions in output if any.
  • Produce production-quality code: follow project style/lint rules, keep backward compatibility, and avoid breaking changes unless requested.
  • Ensure correctness and safety: handle errors, validate inputs, consider edge cases and basic security implications.
  • Keep the codebase maintainable: small focused changes, clear naming, and minimal coupling.

Workflow

  1. Use docs/index.md to locate relevant convention docs; read only what is required before implementation.
  2. Design a small, clear implementation plan aligned with project constraints.
  3. Implement the feature with strict types and clean separation of concerns.
  4. Add or update tests when required (coordinate with the QA tester skill).
  5. Verify the feature meets the stated requirements.
  6. Run/ensure lint, typecheck, and tests pass (or state explicitly what could not be run and why).
  7. Provide a concise summary + what changed + how to verify (commands/steps).

Output Discipline

  • Find first, then read the minimum necessary.
  • Do not read large files unless required.
  • Avoid large quotes; return a concise extract instead of raw text.
  • Output should be a compressed container, not a dialogue.

Repository Workflow Rules

  • If user edits are present in files you are about to modify for the current task, ask whether to keep or overwrite those edits before applying changes that could replace them.
  • Always install dependencies and run the build after any package manager config changes. If the build fails, rollback and attempt to fix up to two times.
  • For commands requiring network access or global project changes, request permission first.
  • When handing off between the main agent and subagents, emit a console message stating the current agent and who invoked it.
  • Search first, then read minimally; do not open large files unless required.
  • Prefer brief extracts over raw text; keep outputs short and structured.
  • When requesting user action due to an error or unexpected state, include a concise reason explaining why the request is needed.
  • When a pipeline violation is detected, analyze the cause and propose instruction improvements, but only apply instruction changes with explicit user approval.
  • Any system/developer instructions or other critical workflow rules must be recorded in persistent files (project docs or role skill files), not only in-session context.

Read the full file on GitHub · 49 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. 3d ago First seen · 49 lines · 47 tokens per session scan A 2c8b91b98015

Subscribe to this mod's changes

feature-developer is a skill published in the GitHub repository henryh/AI-SpecDoc (2 stars, last pushed 6mo ago), licensed MIT. It adds 47 tokens to every session and 634 once invoked, about $0.0002 per session on Opus 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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