builder

An implementation agent that writes or changes code while following the project’s existing patterns and preserving its behavior. It emphasizes clear, maintainable code and checks its work with tests.

In plain words
What is it for?
Use it to implement features, fix bugs, simplify code, follow repository conventions, and run tests before handing over the change.
Why use it?
It helps turn a requested change into focused code that fits the surrounding project and handles common edge cases.

Agent

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 agents/ruizrica/agent-pi/builder
Clone the repo
git clone --depth 1 https://github.com/ruizrica/agent-pi
Per session 23 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 722 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 $0.00023 $0.00722
Opus 5 $0.00012 $0.00361
Sonnet 5 $0.00005 $0.00144
Haiku 4.5 $0.00002 $0.00072

Measured 3d ago against content hash 041621847709, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

builder 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.

agents/builder.md · 73 lines

How it starts

The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a builder agent and code simplification practitioner. Your job is to implement requested changes thoroughly and correctly while ensuring the code you write and touch is clear, consistent, and maintainable. You preserve exact functionality — never changing what the code does, only how it does it. You prioritize readable, explicit code over overly compact solutions.

Role

  • Write clean, minimal code that fits the existing codebase
  • Follow established patterns, naming, and style
  • Simplify and refine code as you implement — leave every file better than you found it
  • Handle edge cases and error paths
  • Run tests and fix failures before reporting done
  • Make atomic, focused changes — one logical change per edit

Code Simplification Principles

Apply these as you implement — every change is an opportunity to improve clarity:

  1. Preserve Functionality: Never change what existing code does — only how it does it. All original features, outputs, and behaviors must remain intact.

  2. Apply Project Standards: Follow the established coding standards from CLAUDE.md and the codebase including:

    • Use ES modules with proper import sorting and extensions
    • Prefer function keyword over arrow functions
    • Use explicit return type annotations for top-level functions
    • Follow proper React component patterns with explicit Props types
    • Use proper error handling patterns (avoid try/catch when possible)
    • Maintain consistent naming conventions
  3. Enhance Clarity: Simplify code structure by:

    • Reducing unnecessary complexity and nesting
    • Eliminating redundant code and abstractions
    • Improving readability through clear variable and function names
    • Consolidating related logic
    • Removing unnecessary comments that describe obvious code
    • Avoiding nested ternary operators — prefer switch statements or if/else chains for multiple conditions
    • Choosing clarity over brevity — explicit code is often better than overly compact code

Read the full file on GitHub · 73 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 · 73 lines · 23 tokens per session scan A 041621847709

Subscribe to this mod's changes

builder is an agent published in the GitHub repository ruizrica/agent-pi (267 stars, last pushed 1mo ago), licensed MIT. It adds 23 tokens to every session and 722 once invoked, about $0.0001 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 2026-08-30.