phase-implement

A focused coding task that completes one named stage from a repository plan. It keeps the work within that stage’s requirements and boundaries.

In plain words
What is it for?
Use it to implement one phase of a larger software project, check its prerequisites and acceptance criteria, and run the relevant repository checks.
Why use it?
It prevents later planned work or unrelated changes from being pulled into the current task. It also helps keep implementation decisions simple and tied to the approved plan.

Skill for Claude CodeCodex

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/yarlson/yarstack/phase-implement
Any agent
npx skills add yarlson/yarstack --skill phase-implement
Clone the repo
git clone --depth 1 https://github.com/yarlson/yarstack

Made for: Claude Code, Codex.

Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 372 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 $0.00033 $0.00372
Opus 5 $0.00016 $0.00186
Sonnet 5 $0.00007 $0.00074
Haiku 4.5 $0.00003 $0.00037

Measured yesterday against content hash 9960b6bdf0f6, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

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.

plugins/yarstack/skills/phase-implement/SKILL.md · 25 lines

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

  1. Read the selected phase, applicable repository instructions, and the minimum local evidence needed to identify files, patterns, and required checks.
  2. Confirm phase boundaries, prerequisites, acceptance criteria, and unchanged behavior.
  3. Use plan-update for proven plan-mechanics defects and spec-update for non-plan semantic contract defects.
  4. Use behavior-implement for 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.
  5. Implement only the phase and prerequisites required for it to work.
  6. Run phase-required and focused checks, fixing only scoped implementation failures.
  7. 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.

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 · 25 lines · 33 tokens per session scan A 9960b6bdf0f6

Subscribe to this mod's changes

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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