Skill: Update Documentation

What This Skill Does

Updates existing project documentation to reflect code changes. Handles:

• Detecting which documentation is affected by recent changes
• Updating module documentation (symbols, structure, data flow)
• Updating feature documentation (new behavior, changed flows)
• Updating the project overview (new modules, changed architecture)
• Ensuring cross-references remain valid

When to Use

• After implementing a feature or fixing a bug that changes behavior
• After refactoring that affects module structure or symbols
• When the user says documentation is "outdated" or asks to "update docs"
• After a plan phase is completed and code has changed

Do NOT use this skill to create documentation from scratch - use generate-docs instead.

Execution Model

• The primary agent spawns doc-explorer. doc-explorer maps code changes to docs and updates files under docs/.
• Rationale: doc updates are grounded in repo state; exploration + edits belong together to avoid losing "why this section changed".
• For large change sets affecting multiple modules, doc-explorer self-delegates per module (see Self-Delegation below).
• The primary agent should keep chat output minimal (what docs changed + any gaps).

Self-Delegation

When changes span multiple modules, doc-explorer SHOULD delegate per-module updates to separate doc-explorer instances via the Task tool:

1. Orchestrator instance: Identifies affected modules from git diff, spawns per-module instances
2. Per-module instance: Receives scoped task ("update docs for module X, changes: ..."), reads existing doc, updates it
3. Orchestrator: Updates cross-cutting artifacts (overview, feature docs), validates cross-references

This prevents token bloat from accumulating analysis of all changed modules in a single context.

Workflow

Step 1: Identify What Changed

Determine the scope of changes using one or more methods:

If changes are recent (current session):

• Review the files modified in the current session
• Check git diff for uncommitted changes

If changes are from git history:

• Use git log --oneline -N to see recent commits
• Use git diff <commit>..HEAD --stat to see affected files
• For large diffs, self-delegate per-module analysis

If the user specifies what changed:

• Focus on the modules/features the user mentions

Step 2: Map Changes to Documentation

For each changed file, determine:

1. Which module does it belong to? → Update docs/modules/<module>.md
2. Which features does it affect? → Update docs/features/<feature>.md
3. Does it change the project structure? → Update docs/overview.md

For changes spanning multiple modules, self-delegate per-module updates.

Step 3: Read Existing Documentation

Read the affected documentation files. Compare against the current code state:

• Are symbols still accurately described?
• Has the module structure changed (new files, moved files)?
• Have dependencies changed?
• Are data flows still correct?
• Are feature behaviors still accurately described?

Step 4: Apply Updates

Update each affected document:

Module Documentation:

• Update Key Symbols if exports changed
• Update Structure if files were added/removed/moved
• Update Dependencies if new dependencies were introduced
• Update Data Flow if processing logic changed
• Keep inventories in sync (files/dirs + symbols)

Feature Documentation:

• Update User Flow if user-facing behavior changed
• Update Technical Flow if implementation approach changed
• Update Implementation table with new/changed symbols
• Update Edge Cases if new limitations discovered

Project Overview:

• Update Modules table if modules were added/removed
• Update Features table if features were added/removed
• Update Architecture if high-level structure changed
• Update Tech Stack if new technologies introduced

Step 5: Validate Cross-References

• Check that all module links in the overview point to existing files
• Check that feature docs reference the correct module docs
• If implementation plans exist, verify they still reference current module documentation
• Remove references to deleted modules/features

Step 6: Report Changes

Present a summary:

• Which documents were updated
• What sections changed
• Any gaps found (new code that has no documentation)

Rules

1. Never overwrite without reading first: Always read existing documentation before modifying.
2. Preserve manual additions: If a section was manually enriched beyond what auto-generation would produce, preserve those additions.
3. Incremental updates: Only update what changed. Don't regenerate entire documents.
4. Track the update: Update the frontmatter version or add a note if the template supports it.
5. No built-in explore agent: Do NOT use the built-in explore subagent type. Self-delegate to doc-explorer instead.
6. Self-delegate for scale: For large change sets spanning multiple modules, spawn additional doc-explorer instances per module via the Task tool.
7. Flag gaps: If new code lacks documentation, notify the user rather than silently ignoring it.
8. File-based interface: All updates are written to files in the docs/ directory. Do not return updated content as chat messages.

Templates

This skill includes normative templates as bundled files. Only read the templates when processing them. Output MUST preserve template headings/frontmatter keys when updating docs:

• tpl-project-overview.md - Expected structure for project overview
• tpl-module-documentation.md - Expected structure for module documentation
• tpl-feature-documentation.md - Expected structure for feature documentation