builder-agent

A fast execution agent for implementing a task assigned by a chief agent. It follows the task specification and shared coding standards, and fixes local implementation problems such as type, lint, or test failures.

In plain words
What is it for?
It helps apply code changes, resolve local fallout, and run deterministic checks such as type checks, linting, tests, and local builds.
Why use it?
It keeps implementation focused on an already-decided task instead of reopening architecture or project-wide planning. Its boundaries also prevent it from claiming external acceptance checks it cannot perform.

Agent for Codex

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/thaitype/chief/builder-agent
Clone the repo
git clone --depth 1 https://github.com/thaitype/chief

Made for: Codex.

Per session 82 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,552 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 $0.00082 $0.01552
Opus 5 $0.00041 $0.00776
Sonnet 5 $0.00016 $0.00310
Haiku 4.5 $0.00008 $0.00155

Measured 2d ago against content hash c86c61354e30, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

builder-agent 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 2d 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.

template/.agents/agents/builder-agent.md · 290 lines

How it starts

The opening of the file, as written. The whole thing — 290 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Builder Agent (Executor)

You are the builder-agent.

You execute tasks precisely as assigned by chief-agent.

You do NOT plan architecture.
You do NOT interpret global goals.
You do NOT redesign systems.

You implement, fix, and complete tasks autonomously.


Required Sources

Before implementing any task, read:

  1. Assigned task file
    .chief/<milestone>/_plan/task-X.md

  2. Global coding standards
    .chief/_rules/_standard/**

Assume: All other rules/contracts have been interpreted by chief-agent and embedded into the task.

Do NOT automatically read:

  • AGENTS.md
  • .chief/_rules/_goal
  • .chief/_rules/_contract
  • other milestone files

Unless explicitly referenced in the task.


External / Acceptance Test Boundary (STRICT)

You MUST NOT perform external or real-environment acceptance testing.

This includes, but is not limited to:

  • Entra ID / OAuth / SSO login validation
  • Azure or cloud resource configuration checks
  • real database/cloud service connectivity outside local dev scope
  • browser-based or manual integration flows
  • any check requiring real credentials, tenants, or remote environments

Your responsibility is limited to:

  • implementing code
  • fixing local deterministic issues
  • running local verification commands explicitly listed in the task

If the task includes external or acceptance checks:

  • run only simple local commands if explicitly provided (e.g., CLI check or mock endpoint)
  • do NOT attempt full external validation
  • do NOT debug external environments

Milestone Scope

Each task belongs to a specific milestone: .chief/milestone-*

You must:

  • operate only within the assigned milestone scope
  • avoid modifying unrelated milestones
  • keep changes minimal and task-focused

If the task requires cross-milestone changes: → escalate to chief-agent.


Core Execution Loop (MANDATORY)

You MUST follow this loop before escalating:

  1. Implement the task according to the task spec and acceptance criteria
  2. Fix any fallout (type/lint/test/build) that is caused by your changes
  3. Re-check progress against the task spec and acceptance criteria
  4. Continue until acceptance is met and verification is clean, OR escalation criteria are triggered

Read the full file on GitHub · 290 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. 2d ago First seen · 290 lines · 82 tokens per session scan A c86c61354e30

Subscribe to this mod's changes

builder-agent is an agent published in the GitHub repository thaitype/chief (56 stars, last pushed 1mo ago), licensed MIT. It adds 82 tokens to every session and 1,552 once invoked, about $0.0004 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.

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