phase-validate

A check of one completed development phase against its authoritative requirements. It compares each acceptance criterion, invariant, failure case, and required check with the implementation and supporting evidence.

In plain words
What is it for?
Use it after implementation to inspect changed files and tests, fix only gaps required by the contract, and run the final authoritative validation command.
Why use it?
It helps reveal missing behavior, incorrect assumptions, cleanup problems, or weak tests before the phase is considered complete.

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

Made for: Claude Code, Codex.

Per session 37 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 374 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 $0.00037 $0.00374
Opus 5 $0.00018 $0.00187
Sonnet 5 $0.00007 $0.00075
Haiku 4.5 $0.00004 $0.00037

Measured 2d ago against content hash 88d918da7471, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

phase-validate 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.

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

What it actually says

Phase Validation

Own contract validation between implementation and structural review.

Workflow

  1. Read the authoritative contract and applicable repository rules unconditionally.
  2. Enumerate each observable acceptance criterion, invariant, required progress, environmental assumption, and failure case, then map it to implementation and evidence.
  3. Inspect changed files, tests, failure paths, cleanup, side effects, and required checks without trusting implementation claims. Confirm that each evidence method fits the relevant input, state, ordering, and failure space.
  4. Invoke focused review skills only when their trigger materially applies; consume read-only findings and keep fixes under this phase's authority. Use separately authorized specialist or independent challenge passes only to broaden defect discovery, verify their claims from evidence, and never treat agreement as proof.
  5. Use plan-update or spec-update when the contract is incorrect or incomplete. Do not invent behavior.
  6. Fix only implementation gaps required by the selected contract.
  7. Run focused checks while correcting, then run the authoritative required command once against final content.

For every criterion report VERIFIED, NOT VERIFIED, or INCONCLUSIVE, with evidence and reasoning. Independence means fresh evidence-based conclusions, not mandatory separate-agent execution.

Do not add verification dependencies or harnesses without authority; report the expected benefit and residual risk when they are unavailable. Do not perform broad maintainability refactoring, final closeout, shipping, commits, pushes, external mutations, or unrelated cleanup. Use phase-review after validation for structural regressions.

Finish when every criterion has a supported status, scoped defects are fixed, required checks reflect final content, and blockers are explicit.

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 · 25 lines · 37 tokens per session scan A 88d918da7471

Subscribe to this mod's changes

phase-validate is a skill published in the GitHub repository yarlson/yarstack (3 stars, last pushed 4d ago), licensed MIT. It adds 37 tokens to every session and 374 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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