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.
npx agentmods add skills/howells/arc/implementnpx skills add howells/arc --skill implementgit clone --depth 1 https://github.com/howells/arcWhat 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 | $0.00054 | $0.03149 |
| Opus 5 | $0.00027 | $0.01574 |
| Sonnet 5 | $0.00011 | $0.00630 |
| Haiku 4.5 | $0.00005 | $0.00315 |
Grade A, and why
implement 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.
How it starts
The opening of the file, as written. The whole thing — 271 lines — stays where its author put it; the contents beside it link to each section on GitHub.
<tool_restrictions>
Use the available user-question mechanism for decisions; unattended, the documented fallbacks in each step govern. EnterPlanMode and ExitPlanMode are
banned because Arc owns its planning and execution process.
</tool_restrictions>
<arc_runtime>
Requires the full Arc bundle. Arc-owned paths (agents/, references/, disciplines/, templates/, scripts/, rules/, skills/) resolve from the plugin root — the directory containing agents/ and skills/. Everything else is the user's repository.
</arc_runtime>
<required_reading> Read before execution:
references/implementation-assurance.md— posture, ownership, review, verification ladderreferences/task-granularity.md— normative XML and legacy compatibilityreferences/testing-patterns.md— seams and work-kind evidencereferences/checkpoint-patterns.md— genuine human gatesreferences/subagent-statuses.md— result-to-state mappingreferences/arc-paths.md— artifact locationsreferences/plan-lifecycle.md— baseline, drift, resumption, index writes
Load when relevant:
references/model-strategy.mdbefore delegating.disciplines/subagent-driven-development.mdbefore using slice owners.disciplines/verification-before-completion.mdbefore completion claims.disciplines/finishing-a-development-branch.mdbefore shipping.references/index.md— the full reference catalogue, when the work needs background you can't name a file for. </required_reading>
<available_agents>
| Agent | Default use |
|---|---|
agents/build/implementer.md |
Own a coherent implementation slice end-to-end. |
unit-test-writer, integration-test-writer, e2e-test-writer |
Conditional complex harness, fixture, browser/E2E, or test-suite work. |
debugger, fixer |
An observed failing test, typecheck, or lint result. |
test-runner, e2e-runner |
Verbose or iterative focused execution when useful. |
agents/build/spec-reviewer.md |
Sonnet whole-implementation spec/completion axis. |
agents/build/code-reviewer.md |
Sonnet whole-implementation standards/evidence axis. |
agents/review/security-engineer.md, agents/review/data-engineer.md, agents/review/performance-engineer.md, agents/review/mastra-agent-engineer.md, agents/review/daniel-product-engineer.md, agents/review/accessibility-engineer.md |
Conditional Guarded specialists, matched to the risk that raised assurance. |
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.
- 2d ago First seen · 271 lines · 54 tokens per session scan A bc0ccd792405
implement is a skill published in the GitHub repository howells/arc (25 stars, last pushed 18d ago), licensed MIT. It adds 54 tokens to every session and 3,149 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 2026-08-30.
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