feature-dev

feature-dev is a skill for Claude Code from euxx/claude-skills-for-copilot. It costs 33 tokens per session (1,940 once invoked), scanned A, original, MIT.

A structured approach to implementing a significant software feature. It covers understanding the codebase, clarifying unclear requirements, designing the architecture, implementing the change, and reviewing it.

In plain words
What is it for?
Use it when starting a new feature or making a substantial change that requires codebase discovery, design work, implementation, and review.
Why use it?
Large feature requests often hide unanswered questions and can lead to changes that do not fit the existing code. This process makes those decisions explicit before and during implementation.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter. Also seen: mentions CLAUDE.md; mentions subagents; mentions AGENTS.md.

Good fit Use it when starting a new feature or making a substantial change that requires codebase discovery, design work, implementation, and review.

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Install with agentmods
npx agentmods add skills/euxx/claude-skills-for-copilot/feature-dev
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 euxx/claude-skills-for-copilot --skill feature-dev
Clone the repo
git clone --depth 1 https://github.com/euxx/claude-skills-for-copilot

Made for: Claude Code.

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-dev

README.md
[![agentmods](https://agentmods.dev/badge/skills/euxx/claude-skills-for-copilot/feature-dev.svg)](https://agentmods.dev/skills/euxx/claude-skills-for-copilot/feature-dev)
Your own site
<a href="https://agentmods.dev/skills/euxx/claude-skills-for-copilot/feature-dev"><img src="https://agentmods.dev/badge/skills/euxx/claude-skills-for-copilot/feature-dev.svg" alt="Measured on agentmods" height="20"></a>
Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,940 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.
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 $0.00033 $0.01940
Opus 5 $0.00016 $0.00970
Sonnet 5 $0.00007 $0.00388
Haiku 4.5 $0.00003 $0.00194

Measured 8d ago against content hash 40a758ce5904, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

feature-dev 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 8d 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-dev/SKILL.md · 196 lines

How it starts

The opening of the file, as written. The whole thing — 196 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Feature Development

You are helping a developer implement a new feature. Follow a systematic approach: understand the codebase deeply, identify and ask about all underspecified details, design elegant architectures, then implement.

Core Principles

  • Ask clarifying questions: Identify all ambiguities, edge cases, and underspecified behaviors. Ask specific, concrete questions rather than making assumptions. Wait for user answers before proceeding. Ask questions early — after understanding the codebase, before designing.
  • Understand before acting: Read and comprehend existing code patterns first.
  • Read files identified by agents: When launching agents, ask them to return lists of the most important files to read. After agents complete, read those files to build detailed context before proceeding.
  • Simple and elegant: Prioritize readable, maintainable, architecturally sound code.
  • Use a todo list: Track all progress throughout.

Phase 1: Discovery

Goal: Understand what needs to be built.

Initial request: $ARGUMENTS

Actions:

  1. Create a todo list with all phases.
  2. If the feature is unclear, ask the user:
    • What problem are they solving?
    • What should the feature do?
    • Any constraints or requirements?
  3. Summarize understanding and confirm with user.

Phase 2: Codebase Exploration

Goal: Understand relevant existing code and patterns at both high and low levels.

Actions:

  1. Launch 2–3 code-explorer sub-agents in parallel. Each agent should:

    • Trace through the code comprehensively, focusing on abstractions, architecture, and flow of control.
    • Target a different aspect of the codebase (e.g. similar features, high-level architecture, user experience, testing patterns).
    • Return a list of 5–10 key files to read.

    Example prompts:

    • "Find features similar to [feature] and trace through their implementation comprehensively"
    • "Map the architecture and abstractions for [feature area], tracing through the code comprehensively"
    • "Analyze the current implementation of [existing feature/area], tracing through the code comprehensively"
    • "Identify UI patterns, testing approaches, or extension points relevant to [feature]"

Read the full file on GitHub · 196 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. 8d ago First seen · 196 lines · 33 tokens per session scan A 40a758ce5904

Subscribe to this mod's changes

feature-dev is a skill published in the GitHub repository euxx/claude-skills-for-copilot (4 stars, last pushed 2mo ago), licensed MIT. It adds 33 tokens to every session and 1,940 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.