A coding workflow assistant for implementing features, fixing code, or restructuring a project. It uses TDD, meaning tests are written and made to pass through a red, green, and refactor cycle.

Use it to build features, debug, refactor without changing behaviour, optimise after measuring, and run the project's verification checks.

It gives implementation work a fixed path from understanding the code and writing a plan to testing and final verification.

builder — Skill by grimoire-rs

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 skills/grimoire-rs/grimoire/builder

Any agent

npx skills add grimoire-rs/grimoire --skill builder

Clone the repo

git clone --depth 1 https://github.com/grimoire-rs/grimoire

Made for: Claude Code, Codex.

Per session 40 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 615 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.

Model	Per session	Once invoked
Fable 5	$0.00040	$0.00615
Opus 5	$0.00020	$0.00308
Sonnet 5	$0.00008	$0.00123
Haiku 4.5	$0.00004	$0.00061

Measured 3d ago against content hash b64d1edd5b8e, 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.

.claude/skills/builder/SKILL.md · 62 lines

How it starts

The opening of the file, as written. The whole thing — 62 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Builder — Senior Implementation Agent

Role: turn plans into working, tested, production-ready Grimoire code.

Workflow

Follow contract-first TDD phases in .claude/rules/workflow-feature.md:

Understand — Load relevant subsystem rules (auto-load on matching paths; load explicit for cross-subsystem work). Grep before invent.
Stub — Signatures + unimplemented!(). Gate: cargo check.
Implement — Fill bodies till spec tests pass.
Verify — task verify before mark complete.

Focus Modes

Implementation (default) — write code per spec
Debugging — reproduce → isolate → trace → fix → regression test
Refactoring — structure only, behavior unchanged (Two Hats Rule, see quality-core.md)
Optimization — measure first, optimize, measure after

Relevant Rules (load explicit for planning)

.claude/rules/quality-core.md + quality-rust.md — universal + Rust quality gates
.claude/rules/workflow-feature.md — TDD phases
.claude/rules/subsystem-cli.md — command pattern, output layer
.claude/rules/subsystem-cli-api.md — report data layer conventions
.claude/rules/subsystem-file-structure.md — storage layout constraints
.claude/rules/arch-principles.md — pattern catalog (auto-load on Rust files)

Tool Preferences

Context7 MCP (mcp__context7__resolve-library-id + mcp__context7__get-library-docs) — query current crate APIs (tokio, oci-client, clap, serde, …) before guess. Training-data API knowledge decay fast.
Sequential Thinking — structured debug of complex bug reports.
task runner — never run ad-hoc cargo/pytest when task command exists. task --list to discover.

Constraints

NO placeholders or TODOs — ship complete changes
NO assume dependencies — Grep first
NO duplicate implementations — check existing code first
ALWAYS cargo fmt before commit; task verify before mark complete
Commit on feature branch only; human decide when to push

Handoff

Read the full file on GitHub · 62 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.

3d ago First seen · 62 lines · 40 tokens per session scan A b64d1edd5b8e

Subscribe to this mod's changes

builder is a skill published in the GitHub repository grimoire-rs/grimoire (8 stars, last pushed 3d ago), licensed Apache-2.0. It adds 40 tokens to every session and 615 once invoked, about $0.0002 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.

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