---
name: reverse-document
description: "Generate missing design or architecture docs from existing implementation — works backwards from code and prototypes."
argument-hint: "<type> <path> (e.g., 'design src/gameplay/combat' or 'architecture Assets/Scripts/Core')"
user-invocable: true
allowed-tools: Read, Glob, Grep, Write, Edit, Bash(bash "*/.claude/skills/reverse-document/../../hooks/yaml-helper.sh" resolve_config *)
model: sonnet
# Read-only diagnostic skill — no specialist agent delegation needed
---

# Reverse Documentation

This skill analyzes existing implementation (code, prototypes, systems) and generates
appropriate design or architecture documentation. Use this when:
- You built a feature without writing a design doc first
- You inherited a codebase without documentation
- You prototyped a mechanic and need to formalize it
- You need to document "why" behind existing code

---

## Workflow

## Phase 1: Parse Arguments

**Format**: `/reverse-document <type> <path>`

**Type options**:
- `design` → Generate a game design document (GDD section)
- `architecture` → Generate an Architecture Decision Record (ADR)
- `concept` → Generate a concept document from prototype

**Path**: Directory or file to analyze, under the code root — `src/` Godot,
`Assets/` Unity, `Source/<Module>/` Unreal (`.claude/docs/code-root-resolution.md`)
- `src/gameplay/combat/` → All combat-related code (Godot)
- `Assets/Scripts/Core/EventSystem.cs` → Specific file (Unity)
- `Source/MyGame/Private/AI/` → A module folder (Unreal)
- `prototypes/stealth-mech/` → Prototype directory

!`bash "${CLAUDE_SKILL_DIR}/../../hooks/yaml-helper.sh" resolve_config --keys workflow,system_overrides,automation`

**Automation mode**: Resolve `modes.automation` (`project.local.yaml` →
`project.yaml` → default `collaborative`). Every `AskUserQuestion` call and
every file write follows `.claude/docs/automation-modes.md`
(collaborative asks always · guided major-only · autonomous logs and proceeds;
`automation_always_ask` categories always prompt).

Resolved above — use as-is. No block → defaults in
`.claude/docs/config-resolution.md`.

**Resolve the workflow tier** for the target system: map `<path>` to a system
name, then use the `system_overrides` row for that system if the block above
lists one, else the project `workflow` value. It sets how much document is
generated — see Phase 5. Semantics of each tier are in
`.claude/docs/workflow-modes.md`.

> **Resolve the tier — do not assume it.** "Resolve the tier per
> `workflow-modes.md`" with no bootstrap names a resolution it gives no way to
> perform: that document defines what each tier *means*, but it cannot say what
> *this project* is set to. The consequence is large here — at `full` this skill
> writes an 8-section GDD and at `minimal` a one-page brief, so a wrong tier
> produces the wrong artifact entirely.

**Examples**:
```bash
/reverse-document design src/gameplay/magic-system
/reverse-document architecture Source/MyGame/Private/EntityComponent
/reverse-document concept prototypes/vehicle-combat
```

## Phase 2: Analyze Implementation

**Read and understand the code/prototype**:

**For design docs (GDD):**
- Identify mechanics, rules, formulas
- Extract gameplay values (damage, cooldowns, ranges)
- Find state machines, ability systems, progression
- Detect edge cases handled in code
- Map dependencies (what systems interact?)

**For architecture docs (ADR):**
- Identify patterns (ECS, singleton, observer, etc.)
- Understand technical decisions (threading, serialization, etc.)
- Map dependencies and coupling
- Assess performance characteristics
- Find constraints and trade-offs

**For concept docs (prototype analysis):**
- Identify core mechanic
- Extract emergent gameplay patterns
- Note what worked vs what didn't
- Find technical feasibility insights
- Document player fantasy / feel

## Phase 3: Ask Clarifying Questions

**DO NOT** just describe the code. **ASK** about intent:

**Design questions**:
- "I see a [resource] system that depletes during [activity]. Was this for:
  - Pacing (prevent spam)?
  - Resource management (strategic depth)?
  - Or something else?"
- "The [mechanic] seems central. Is this a core pillar, or supporting feature?"
- "[Value] scales exponentially with [factor]. Intentional design, or needs rebalancing?"

**Architecture questions**:
- "You're using a service locator pattern. Was this chosen for:
  - Testability (mock dependencies)?
  - Decoupling (reduce hard references)?
  - Or inherited from existing code?"
- "I see manual memory management instead of smart pointers. Performance requirement, or legacy?"

**Concept questions**:
- "The prototype emphasizes stealth over combat. Is that the intended pillar?"
- "Players seem to exploit the grappling hook for speed. Feature or bug?"

## Phase 3b: Sufficiency Check — is there enough here to document?

**Run this before Phase 4, and stop here if it fails.** This skill infers a
design from an implementation, so when the implementation is thin there is
nothing to infer *from* — and the template below will happily accept invented
content, because every section of it is mandatory.

Count what Phase 2 actually found:

| Signal | What counts |
|---|---|
| Mechanics | A named behaviour with observable rules — not a stub, not an empty class |
| Formulas | An expression computing a gameplay value from inputs |
| Values | A tuning constant with a use site |

**If all three counts are zero, or the target path holds fewer than ~20 lines of
non-boilerplate code, stop and say so:**

> "`[path]` does not contain enough implementation to reverse-document.
> Found: [N] mechanics, [N] formulas, [N] tuning values.
> Reverse-documentation infers design from behaviour; with no behaviour to read,
> anything I produce would be invention wearing the format of a design document.
> If the design exists only in your head, `/design-system [name]` is the skill
> that captures it — it asks rather than infers."

**Do not proceed on a partial count by filling the rest.** A path with two
mechanics and no formulas gets a document with two mechanics and an explicit
`FORMULAS DISCOVERED: none found in the source` — see Phase 4.

## Phase 4: Present Findings

Before drafting, show what you discovered:

```
I've analyzed [path]/. Here's what I found:

MECHANICS IMPLEMENTED:
- [mechanic-a] with [property] (e.g. timing windows, cooldowns)
- [mechanic-b] (e.g. interaction between two states)
- [resource] system (depletes on [action], regens on [condition])
- [state] system (builds up, triggers [effect])

FORMULAS DISCOVERED:
- [Output] = [formula using discovered variables]
- [Secondary output] = [formula]

UNCLEAR INTENT AREAS:
1. [Resource] system — pacing or resource management?
2. [Mechanic] — core pillar or supporting feature?
3. [Value] scaling — intentional design or needs tuning?

Before I draft the design doc, could you clarify these points?
```

> **Every section above may be empty, and an empty one must say so.** Write
> `none found in the source` under the heading — never omit the heading (which
> reads as "not looked for") and never populate it from what a system like this
> usually has. The bracketed rows are *shapes*, not quotas: a source with one
> mechanic yields one row, not four.
>
> This matters more here than in a report, because the output of this skill is not
> a report — it is a **design document**, and `/design-review`, `/create-epics` and
> `/create-stories` will read it as a statement of authored intent. A fabricated
> formula in a GDD does not stay a documentation error; it becomes a requirement,
> and then a story, and then code written to satisfy it.

Wait for user to clarify intent before drafting.

**If the user does not answer the `UNCLEAR INTENT AREAS` questions, do not draft
the resolved version anyway.** Those questions exist because **code cannot tell
you why** — it records what was built, never what was intended, and the gap
between them is the entire content of a design document. Unanswered items are
carried into the draft verbatim as open questions, in the document, marked
`INTENT UNKNOWN — inferred from implementation, not confirmed`. An inferred
intent presented as a settled one is the failure mode of this whole skill.

## Phase 5: Draft Document Using Template

Based on type, use appropriate template:

| Type | Template | Output Path |
|------|----------|-------------|
| `design` | `templates/design-doc-from-implementation.md` | `design/gdd/[system-name].md` |
| `architecture` | `templates/architecture-doc-from-code.md` | `docs/architecture/[decision-name].md` |
| `concept` | `templates/concept-doc-from-prototype.md` | `prototypes/[name]/CONCEPT.md` or `design/concepts/[name].md` |

**The `design` output scales with the workflow tier** (resolved in Phase 1):
- **`full`** — generate a full 8-section GDD.
- **`standard`** — generate a 5-section GDD (Overview, Detailed Design, Edge Cases,
  Dependencies, Acceptance Criteria; + Formulas when the recovered system defines
  numeric rules). Skip Player Fantasy and Tuning Knobs.
- **`minimal`** — generate a **game brief** in the one-page format
  (`.claude/docs/templates/game-brief.md`), not a GDD. For the whole game write
  `design/game-brief.md`; for a single reverse-engineered system write
  `design/[system-name]-brief.md`.

(`architecture` and `concept` outputs are tier-independent.)

**Draft structure**:
- Capture **what exists** (mechanics, patterns, implementation)
- Document **why it exists** (intent clarified with user)
- Identify **what's missing** (edge cases not handled, gaps in design)
- Flag **follow-up work** (balance tuning, missing features)

### Stamp the provenance — required, at the top of every document this skill writes

A document produced here lands at the same path, in the same format, as one a
designer wrote by hand, and **every downstream consumer treats the two
identically**. `/design-review` checks it for completeness, `/create-epics`
derives epics from it, `/create-stories` turns its lines into acceptance
criteria. Nothing anywhere asks where it came from.

The difference is not cosmetic: an authored GDD states **intent**, and this one
states **observed behaviour plus inference**. When they disagree, the code is
what needs changing in the first case and the document in the second — and a
reader cannot tell which they are holding unless the document says.

Emit this immediately under the title:

```markdown
> **Reverse-documented from implementation** — generated by `/reverse-document`
> from `[path]` on `[date]`, at commit `[short-sha]`.
> This records what the code **does**; intent marked `INTENT UNKNOWN` below was
> inferred, not confirmed by the author. Where this document and the code
> disagree, do not assume the document is the requirement.
```

Keep the banner on revision. If a human later confirms the intent and adopts the
document as authored design, removing it is their explicit act — not a
side effect of the next edit.

## Phase 6: Show Draft and Request Approval

**Collaborative protocol**:
```
I've drafted the [system-name] design doc based on your code and clarifications.

[Show key sections: Overview, Mechanics, Formulas, Design Intent]

ADDITIONS I MADE:
- Documented [mechanic] as "[intent]" per your clarification
- Added edge cases not in code (e.g., what if [resource] hits 0 mid-[action]?)
- Flagged balance concern: [scaling type] scaling at [boundary condition]

SECTIONS MARKED AS INCOMPLETE:
- "[System] interaction with [other-system]" (not fully implemented yet)
- "[Variant or feature]" (only [subset] implemented so far)

May I write this to [output path]?
```

Use the tier-correct output path in the prompt: `design/gdd/[system-name].md` for
a `full`/`standard` GDD, or `design/[system-name]-brief.md` for a `minimal` brief.

**At `collaborative`** — wait for approval; the user may request changes before
writing. **At `guided`** — this is a *new* file, so `automation-modes.md:81`
still has it asked ("May I write?" is asked for new files only); if the target
already exists, present the diff and proceed without waiting for an explicit
"yes". **At `autonomous`** — write and log the decision.

> **Keep this line scoped to its mode.** The skill header defers every file
> write to `automation-modes.md`, so an unconditional "wait for approval" here
> collides with it at both `guided` and `autonomous`. Same class as
> `/map-systems` Step 5b.

## Phase 7: Write Document with Metadata

When approved, write the file with special markers:

```markdown
---
status: reverse-documented
source: [path/]
date: [today]
verified-by: [User name]
---

# [System Name] Design

> **Note**: This document was reverse-engineered from the existing implementation.
> It captures current behavior and clarified design intent. Some sections may be
> incomplete where implementation is partial or intent was unclear.

[Rest of document...]
```

## Phase 8: Flag Follow-Up Work

After writing, suggest next steps:

```
✅ Written to design/gdd/combat-system.md

FOLLOW-UP RECOMMENDED:
1. Run /balance-check on combat formulas (exponential scaling concern)
2. Create ADR for stamina system architecture decision
3. Implement missing edge cases:
   - Stamina depletion mid-combo behavior
   - Stagger state during dodge
4. Extend design doc when weapon variety is implemented

Would you like me to tackle any of these now?
```

---

## Template Selection Logic

| If analyzing... | Use template... | Because... |
|----------------|-----------------|------------|
| `<code root>/gameplay/*` | design-doc-from-implementation.md | Gameplay mechanics → GDD |
| `<code root>/core/*`, `<code root>/ai/*` | architecture-doc-from-code.md | Core systems → ADR |
| `prototypes/*` | concept-doc-from-prototype.md | Experiments → concept doc |
| `<code root>/networking/*` | architecture-doc-from-code.md | Technical systems → ADR |
| `<code root>/ui/*` | design-doc-from-implementation.md | UI/UX → design spec |

---

## Example Session: Reverse-Document a System

```
User: /reverse-document design <code root>/gameplay/[system]

Agent: I'll analyze your [system] implementation to create a design doc.
       [Reads code, discovers mechanics, formulas]

Agent: I've analyzed <code root>/gameplay/[system]/. Here's what I found:
       [Shows mechanics, formulas, unclear areas]

       Before drafting, could you clarify:
       1. [Resource] system intent?
       2. Is [mechanic] a core pillar?
       3. [Value] scaling — intentional or needs tuning?

User: 1. [Resource] is for pacing, prevent [unwanted behavior]
      2. [Mechanic] is core — I want [design intent]
      3. Yeah, exponential is too much, should be linear

Agent: Perfect, that clarifies the vision. Let me draft the design doc.
       [Shows draft with clarified intent]

       May I write this to design/gdd/[system-name].md?

User: Yes, write it.

Agent: ✅ Written to design/gdd/[system-name].md
       ✅ Marked as [REVERSE-DOCUMENTED]
       ✅ Flagged [value] scaling for rebalancing

       Next steps:
       - Update [formula] to [corrected scaling]
       - Run /balance-check to validate [curve]
       - Document [mechanic] as core pillar in game-pillars.md
```

---

## Collaborative Protocol

This skill follows the collaborative design principle:

1. **Analyze First**: Read code, understand implementation
2. **Question Intent**: Ask about "why", not just "what"
3. **Present Findings**: Show discoveries, highlight unclear areas
4. **User Clarifies**: Separate intent from accidents
5. **Draft Document**: Create doc based on reality + intent
6. **Show Draft**: Display key sections, explain additions
7. **Get Approval**: "May I write to [filepath]?" On approval: Verdict: **COMPLETE** — document generated. On decline: Verdict: **BLOCKED** — user declined write.
8. **Flag Follow-Up**: Suggest related work, don't auto-execute

**Never assume intent. Always ask before documenting "why".**