document-writing

This skill is the single home of documentation discipline, serving two consumers from one source. The standard itself — the writing rules, the five-document architecture, the ownership boundaries, and the cross-reference and maintenance rules — lives in documentation-standards.md. Every document-producing agent and skill follows it when authoring; the doc-reviewer enforces it on review, together with the stack-specific checks in review-checks.md — a stack overlay each stack ships beside this skill (the stack-agnostic core source carries none). This file carries the agent obligations and the author's validation checklist. Author and reviewer read the same rulebook.

Agent Guidelines

These rules bind any agent that reads or writes project documentation. They restate the ownership and abstraction boundaries from documentation-standards.md as direct obligations.

Agents must:

• Read PRD requirements before implementing
• Reference system-design.md for types and interfaces
• Check ADRs for design constraints before proposing alternatives
• Never duplicate type definitions across documents
• Never add code or language-specific constructs to PRD
• Never reference internal code in PRD (no class names, function names, or variable names)
• Use behavioral language in PRD ("the system retries the operation" not "Retry() calls continue")
• When PRD needs to reference implementation details, add a link: **Design:** See [system-design.md#section](system-design.md#section)

Validation Checklist

This is the author's self-check before merging a documentation change. The doc-reviewer enforces the same bar at review time, with stack-specific additions, from review-checks.md. Before merging, verify:

Structural Checks

• All requirement IDs have HTML anchors (<a id="req-xx-nnn"></a>)
• No implementation pseudocode in PRD
• No language-specific code blocks in PRD
• No language-specific constructs in PRD
• All cross-references use full paths with anchors
• Tables have headers and consistent column counts
• No relative references ("above", "below", "previous")
• No version numbers in documents
• ADR References use em-dashes
• ADR Implementation section includes Requirements: or Non-goal:
• Code blocks have language tags

Cross-Document Coherence Checks

• Every requirement ID in system-design.md exists in prd.md
• Deprecated requirements are absent from system-design.md
• Constants referenced in prd.md are defined in system-design.md
• Domain terms used in prd.md and system-design.md are defined in ubiquitous-language.md (or added there in the same change)
• All document links resolve to valid anchors

Abstraction Level Checks (system-design.md)

• No struct field tables (| Field | Type | Description | rows). Purpose paragraph plus source pointer instead.
• No function parameter tables (| Parameter | Type | Description | rows). Contract prose plus source pointer instead.
• No constant literal values. Name the constant, cite the source file.
• No exhaustive rule listings (iptables, SQL, shell). State the invariant; source is authoritative for the full listing.
• Self-test: for each paragraph, would a field rename, parameter addition, or constant change in source silently invalidate it? If yes, rewrite or delete.

Structure Within a Document Checks

Per Structure Within a Document:

• Each top-level heading opens with a Level 1 paragraph (≤200 words, narrative prose, no jargon) that states purpose, conclusion, and scope.
• A non-specialist can read the first 200 words of any major section and walk away with a useful understanding.
• No section jumps from Level 1 to Level 3 with more than a 5× length ratio — insert a Level 2 bridge when the gap is larger.
• Each level is self-contained: no forward references ("as explained in Section 3 below") required to understand the current level.
• Lower-level sections may use lists, tables, and diagrams, but Level 1 paragraphs are prose.

Writing Standards Checks

• No prohibited words without data
• No vague adjectives without measurements
• Sentences under 30 words; 70% under 20 words
• No wordy phrases
• Markdown prose is not hard-wrapped to a column; no word is broken across lines with a hyphen (YAML frontmatter >- excepted)
• Every paragraph passes the "So what?" test
• Answers start with the answer
• Acronyms defined on first use
• No subjective language or buzzwords

Reviewing Documents

The doc-reviewer enforces every standard in documentation-standards.md. The stack-specific review checklist — the prohibited-pattern instantiations for this stack, project-specific coherence checks, the review process, and the autofix protocol — lives in review-checks.md, which extends these checks to the stack's concrete paths and constructs. The reviewer loads both files.