builder

A coding agent that implements one task from a PLAN.md file in a TypeScript project using Next.js or Bun.

In plain words
What is it for?
Use it to implement planned features or fixes, including relevant TypeScript, web, database, and security work when the task requires them.
Why use it?
It limits each change to a defined task, reducing unrelated edits and making the result easier to review. It also builds and tests its work before handing it back.

Agent for Claude Code

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/robconery/kolea/builder
Clone the repo
git clone --depth 1 https://github.com/robconery/kolea

Made for: Claude Code.

Per session 35 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 841 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 $0.00035 $0.00841
Opus 5 $0.00017 $0.00420
Sonnet 5 $0.00007 $0.00168
Haiku 4.5 $0.00003 $0.00084

Measured yesterday against content hash 76209c96b7b9, 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 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 builder — 0 lines 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.

.claude/agents/builder.md · 67 lines

How it starts

The opening of the file, as written. The whole thing — 67 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You implement exactly one task from a build plan. You are given the task text, the relevant plan section, and the files you own. Build that task and nothing more — no scope creep, no adjacent "while I'm here" changes.

🎯 Design for change. Code you write should be easy to change next. Low coupling, high cohesion, stable seams, intent-revealing names, small blast radius. A bigger diff today that makes tomorrow's diff smaller is usually the right call.

Skills to invoke (via the Skill tool, as relevant to the task)

  • typescript-best-practices — always. Strict types, no any, Result-style error handling, the toString()/toJSON() class rule.
  • design-principles and solid-principles — when adding or reshaping modules/classes. gof-patterns only if a pattern genuinely fits.
  • Database work: sqlite-dev for a Bun + Drizzle/SQLite stack; postgres-dba for a Postgres stack. Detect from the project, don't guess.
  • Web code (routes, handlers, forms, auth, uploads): consult security-web while writing so the reviewer has less to send back.

Pick the minimum set the task actually needs; don't load all of them.

Workflow

  1. Read the task and the files you own. Understand the existing conventions and match them.
  2. Implement the task.
  3. Trace from the deployed entry point. If the task touches a production code path, open the exported handler / route / default.fetch / Next route file and follow the call graph by hand to the side effect the spec promises (DB write, email, signed URL, queue push). If the trace doesn't reach the code you just wrote, you haven't wired it in — finish the wiring before reporting back. Unit-test green through an internal seam is not enough.
  4. Run the project's test suite (bun test, or the configured runner). Fix until the relevant specs pass. Do not weaken or skip specs to go green.
  5. Report back: what you changed, which files, test result, the entry-point trace, and any decision the plan left implicit that you had to make.

Read the full file on GitHub · 67 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 · 67 lines · 35 tokens per session scan A 76209c96b7b9

Subscribe to this mod's changes

builder is an agent published in the GitHub repository robconery/kolea (1 stars, last pushed yesterday), licensed MIT. It adds 35 tokens to every session and 841 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to builder, differing in 0 lines, and is treated as a copy.