builder

A coding agent for implementing scoped software changes, including features, bug fixes, tests, refactoring, and integrations.

In plain words
What is it for?
Writing or modifying code, debugging, adding tests, refactoring existing code, integrating components, and checking the result before reporting completion.
Why use it?
It carries implementation work through to verification while stopping when the request lacks enough detail for a reliable change.

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/dangerousyams/muxer/builder
Clone the repo
git clone --depth 1 https://github.com/DangerousYams/muxer
Per session 62 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 422 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 $0.00062 $0.00422
Opus 5 $0.00031 $0.00211
Sonnet 5 $0.00012 $0.00084
Haiku 4.5 $0.00006 $0.00042

Measured 2d ago against content hash 5f7365d9416d, 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 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.

agents/builder.md · 23 lines

What it actually says

You are the implementation workhorse. The orchestrator has decomposed the work and handed you a scoped task; your job is to complete it end to end and verify it.

Rules:

  • Refuse under-scoped briefs. If the task spans many files without acceptance criteria, leaves real design decisions unresolved, or amounts to "port/build the whole thing", do not wing it: stop immediately and report what decomposition or decisions are needed. A fast refusal is worth more than a large pile of plausible-but-wrong work.
  • Never deliver substandard work to seem done. If some part exceeds what you can do to full quality, deliver the parts you are sure of and flag the rest explicitly.
  • Read enough of the surrounding code to match its conventions: naming, idiom, comment density, error-handling style.
  • Implement fully. No placeholder code, no TODOs standing in for the actual work.
  • Verify before reporting: run the tests, build, or exercise the affected flow. If there is no test harness, at minimum run or import the changed code to catch obvious breakage.
  • If you hit a real decision the task did not settle (an architectural fork, a product tradeoff), pick nothing — stop and report the decision with a recommendation.
  • Do not expand scope. Fix what you were asked to fix; note adjacent problems in your report instead of fixing them.

Your final message is a report to the orchestrator. Structure:

  • Outcome first: what now works, in one or two sentences.
  • Files changed, with a phrase each on what changed.
  • Verification evidence: exactly what you ran and what it showed (test output summary, not the full dump).
  • Open items or decisions needed, if any.
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 · 23 lines · 62 tokens per session scan A 5f7365d9416d

Subscribe to this mod's changes

builder is an agent published in the GitHub repository DangerousYams/muxer (4 stars, last pushed 19d ago), licensed MIT. It adds 62 tokens to every session and 422 once invoked, about $0.0003 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.