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/yarlson/yarstack/phase-implementnpx skills add yarlson/yarstack --skill phase-implementgit clone --depth 1 https://github.com/yarlson/yarstackWhat 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 | $0.00033 | $0.00372 |
| Opus 5 | $0.00016 | $0.00186 |
| Sonnet 5 | $0.00007 | $0.00074 |
| Haiku 4.5 | $0.00003 | $0.00037 |
Grade A, and why
phase-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 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.
What it actually says
Phase Implementation
Own phase scope and orchestrate only the work required to implement it.
Keep the implementation simple and limited to current requirements. Reuse an existing source of truth when the same rule or knowledge would otherwise be maintained in more than one place, but do not combine unrelated behavior merely because the code looks similar. Add abstractions, flexibility, and configuration only when a concrete current need justifies them.
Workflow
- Read the selected phase, applicable repository instructions, and the minimum local evidence needed to identify files, patterns, and required checks.
- Confirm phase boundaries, prerequisites, acceptance criteria, and unchanged behavior.
- Use
plan-updatefor proven plan-mechanics defects andspec-updatefor non-plan semantic contract defects. - Use
behavior-implementfor product behavior. For engineering tooling and infrastructure, use it only when native checks cannot credibly prove important behavior, concrete complexity or failure risk warrants regression coverage, and a focused deterministic test boundary fits the task. Otherwise implement through the repository-native path and run its applicable checks without adding test infrastructure. - Implement only the phase and prerequisites required for it to work.
- Run phase-required and focused checks, fixing only scoped implementation failures.
- Report implemented behavior, changed scope, checks, alternative evidence, and remaining blockers.
Do not perform independent post-implementation validation, structural review, final closeout, commits, pushes, releases, later phases, or unrelated cleanup. Those remain separate gates unless the user explicitly requests them.
Finish at implementation evidence when the selected phase is complete, required checks pass or are explicitly blocked, and no later-phase work was introduced.
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.
- yesterday First seen · 25 lines · 33 tokens per session scan A 9960b6bdf0f6
phase-implement is a skill published in the GitHub repository yarlson/yarstack (3 stars, last pushed 4d ago), licensed MIT. It adds 33 tokens to every session and 372 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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