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vibe-spec-sync

vibe-spec-sync is a skill for Claude Code from mracal/vibe-engineering. It costs 46 tokens per session (1,613 once invoked), scanned A, a copy of vibe-spec-sync, MIT.

A tool for keeping a project's specification documents, tests, and code in agreement. It checks whether recent code changes have made the written requirements outdated and can update the specification after approved decisions.

In plain words
What is it for?
Use it before commits, after recording decisions, or during periodic checks to compare specifications with implementation code and related tests. It requires an existing Markdown specification and the code it describes.
Why use it?
It prevents the written plan from drifting away from how the software actually works. This reduces confusion about which behavior is current before committing changes.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter. Also seen: names the AskUserQuestion tool.

not rated 3repo 7d ago A scan 46 tokens copy · 100% MIT

Good fit Use it before commits, after recording decisions, or during periodic checks to compare specifications with implementation code and related tests. It requires an existing Markdown specification and the code it describes.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/mracal/vibe-engineering/spec-sync
View source ↗ mracal/vibe-engineering
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.

Any agent
npx skills add mracal/vibe-engineering --skill spec-sync
Clone the repo
git clone --depth 1 https://github.com/mracal/vibe-engineering

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for vibe-spec-sync

README.md
[![agentmods](https://agentmods.dev/badge/skills/mracal/vibe-engineering/spec-sync/github.svg)](https://agentmods.dev/skills/mracal/vibe-engineering/spec-sync)
Your own site
<a href="https://agentmods.dev/skills/mracal/vibe-engineering/spec-sync"><img src="https://agentmods.dev/badge/skills/mracal/vibe-engineering/spec-sync/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for vibe-spec-sync

Your own site · 80×15
<a href="https://agentmods.dev/skills/mracal/vibe-engineering/spec-sync"><img src="https://agentmods.dev/badge/skills/mracal/vibe-engineering/spec-sync.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 46 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,613 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 100% copy Near-identical to another mod 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 5.1 $0.00046 $0.01613
Opus 5.5 $0.00018 $0.00645
Sonnet 5.5 $0.00009 $0.00323
Haiku 4.5 $0.00005 $0.00161

Measured 1mo ago against content hash e1eba302006e, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

vibe-spec-sync 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 1mo 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.

Origin

This is a copy

100% identical to vibe-spec-sync — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/spec-sync/SKILL.md · 147 lines

How it starts

The opening of the file, as written. The whole thing — 147 lines — stays where its author put it; the contents beside it link to each section on GitHub.

vibe-spec-sync

Code changes. Specs don't update themselves. This skill closes the loop.

When to Use This Skill

  • Before committing — detect spec drift from staged changes
  • After approving decisions (from vibe-decision-journal) — sync them back to spec
  • When vibe-spec-vs-code-audit found gaps — fix them
  • Periodically — ensure spec still reflects reality

When NOT to Use This Skill

  • No spec exists (write one first, or use vibe-doc-quality-gate to bootstrap)
  • Prototype/spike code with no spec commitment
  • Spec is explicitly labeled as aspirational/future-state

Prerequisites

The project must have:

  • A specification document (markdown) — configured in step 1
  • Implementation code that the spec describes
  • Optionally: a test suite with requirement traceability markers (# req:[ID])

Steps

Step 1: Locate Spec and Code

  1. Find the spec — Look for:

    • spec.md, SPEC.md, *_spec.md in project root or docs/
    • Design docs in docs/design/, docs/architecture/
    • Ask user if ambiguous: "Which document is the authoritative spec?"

  2. Find the implementation — The code files the spec describes

  3. Find the decision log — docs/decisions/decisions.jsonl (from vibe-decision-journal)

Step 2: Extract Drift from Staged Changes

Run git diff --cached and analyze what changed relative to the spec:

  1. Categorize each change:

    • Spec-aligned: Change matches what the spec says → no action
    • Spec-extending: Change adds behavior the spec doesn't mention → spec needs new section
    • Spec-modifying: Change alters behavior the spec describes differently → spec needs update
    • Spec-contradicting: Change violates what the spec explicitly forbids → flag for review

  2. For each drift item, produce:

    DRIFT-[NNN]:
  Type: extending | modifying | contradicting
  Spec section: "## [Header]"
  Current spec says: "[quoted text]"
  Code now does: "[description of new behavior]"
  Suggested spec update: "[proposed new text]"

Read the full file on GitHub · 147 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.

  1. 1mo ago First seen · 147 lines · 46 tokens per session scan A e1eba302006e

Subscribe to this mod's changes

vibe-spec-sync is a skill published in the GitHub repository mracal/vibe-engineering (3 stars, last pushed 7d ago), licensed MIT. It adds 46 tokens to every session and 1,613 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to vibe-spec-sync, differing in 0 lines, and is treated as a copy.

Code reviewWriting and docsagentic-aiagentic-workflowaiai-agentscodexcodex-cli
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