feature-dev

A guided workflow for adding a feature to an existing codebase. It starts by understanding the project, clarifying unclear requirements, and designing the architecture before implementation.

In plain words
What is it for?
Use it to investigate a codebase, identify affected files, resolve edge cases and missing requirements, choose an implementation design, and then build and validate a feature.
Why use it?
It reduces the risk of building the wrong behavior or fitting a feature poorly into the existing system. The workflow also encourages readable design, progress tracking, and targeted file review.

Command

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 commands/tlipoca9/devgen/feature-dev
Clone the repo
git clone --depth 1 https://github.com/tlipoca9/devgen
Per session 11 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,063 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 100% copy Near-identical to another mod 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 $0.00011 $0.01063
Opus 5 $0.00005 $0.00531
Sonnet 5 $0.00002 $0.00213
Haiku 4.5 $0.00001 $0.00106

Measured yesterday against content hash 93fd24beba5b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, 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 yesterday.

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.

Origin

This is a copy

100% identical to feature-dev — 1 line differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.codebuddy/commands/feature-dev.md · 125 lines

How it starts

The opening of the file, as written. The whole thing — 125 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 with implementation. Ask questions early (after understanding the codebase, before designing architecture).
  • 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 TodoWrite: Track all progress throughout

Phase 1: Discovery

Goal: Understand what needs to be built

Initial request: $ARGUMENTS

Actions:

  1. Create todo list with all phases
  2. If feature unclear, ask user for:
    • 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 agents in parallel. Each agent should:

    • Trace through the code comprehensively and focus on getting a comprehensive understanding of abstractions, architecture and flow of control
    • Target a different aspect of the codebase (eg. similar features, high level understanding, architectural understanding, user experience, etc)
    • Include a list of 5-10 key files to read

    Example agent 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 · 125 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. yesterday First seen · 125 lines · 11 tokens per session scan A 93fd24beba5b

Subscribe to this mod's changes

feature-dev is a command published in the GitHub repository tlipoca9/devgen (5 stars, last pushed 4mo ago), licensed MIT. It adds 11 tokens to every session and 1,063 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to feature-dev, differing in 1 line, and is treated as a copy.