Spec Coder

Structured spec-first development workflow with multi-role expert review gates: clarify requirements, author spec documents (requirements/design/tasks), generate code from spec, verify with real tests, and iterate while keeping spec and code in sync. Use when user wants to build a feature or system with a spec-first approach, mentions "spec coding", "spec-driven development", or asks to write specs before coding.

Spec Coding Workflow

Write specs first, then generate code. 5 phases, each producing artifacts that feed the next. Expert review gates between phases catch issues early.

Session Start

On every new session:

1. Read specs/status.md to identify current phase, active changes, and deferred items.
2. Read phase-relevant spec files — see Quick Reference table below for which artifacts each phase produces/consumes. Skip specs/changes/archive/ — archived changes represent completed/merged work and must not be read or referenced.
3. Confirm with the user which phase/gate to continue from. If mid-phase, summarize progress so far.
4. No specs/status.md? This is a new project — start from Phase 0 (existing codebase) or Phase 1 (greenfield).

Workflow Overview

text

Phase 0 ──→ Phase 1 ──→ ║Gate 1║ ──→ Phase 2a ──→ Phase 2b ──→ ║Gate 2║
(scan)      (clarify)    (req.)       (design)      (preview)     (design)
                                                                     │
    ┌────────────────────────────────────────────────────────────────┘
    ▼
Phase 2c ──→ Phase 2d ──→ ║Gate 3║ ──→ Phase 3 ──→ ║Gate 4║ ──→ Phase 4 ──→ Phase 5
(tasks)      (specs)       (plan)       (code)       (code)       (verify)    (iterate)
                                                                                  │
                                                                    ┌─────────────┘
                                                                    ▼
                                                              Re-trigger Gate
                                                              2 / 3 / 4 based
                                                              on change scope

Gates auto-approve when no Critical/Major issues. See Expert Review Protocol for details.

Quick Reference

Phase	Input	Output	Gate	Next
0. Codebase Scan	codebase files	status.md § Codebase Context	—	Phase 1
1. Clarify & Scope	user requirements + Phase 0 context	requirements.md	Gate 1 (req.)	Phase 2a
2a. Technical Design	requirements.md	design.md	—	Phase 2b
2b. Design Preview	design.md	design-preview/	Gate 2 (design)	Phase 2c
2c. Task Breakdown	design.md + requirements.md	tasks.md	—	Phase 2d
2d. Feature Specs	tasks.md + design.md	spec_xxx.md	Gate 3 (plan)	Phase 3
3. Generate	tasks.md + spec_xxx.md	code + tests	Gate 4 (code)	Phase 4
4. Verify	code + tests + spec_xxx.md	test results, Implementation Map	—	Phase 5 or done
5. Evolve	trunk specs + user request	changes/	scoped gate	→ Phase 1–4

When to Use

Trigger conditions:

• User mentions "spec coding", "spec-first", "spec-driven development"
• User asks to write specs / requirements / design docs before implementation
• User mentions phase keywords: "clarify requirements", "write a spec", "generate from spec"

When NOT to use: Pure bug fixes, one-line config changes, dependency updates, or tasks completable in < 15 minutes without design decisions.

Complexity triage — choose the right track:

Track	When	Phases	Artifacts	Review Depth
Small	Single endpoint, field addition, < 1 hr	Spec (lite) → Generate → Verify	spec_xxx.md only	Lite (1–2 roles, skip if trivial)
Medium	Single feature, 1–4 hrs, 1–3 modules	Clarify (brief) → Spec → Generate → Verify	spec_xxx.md + tasks.md	Standard (2–3 roles)
Large	Multi-module, > 4 hrs, or new system	Full 5-phase workflow	All spec files	Full (all roles)

Ask the user which track fits, or infer from the scope of their request.

Small track shortcut: Skip Phase 1. Write a single spec_xxx.md (Interface + Business Rules + Test Points only), then go straight to Generate → Verify.

Medium track shortcut: Phase 1 is a brief bullet-point confirmation (no full requirements.md). Phase 2 produces tasks.md + spec_xxx.md only (skip design.md and design-preview/ unless architecture decisions are needed).

Mid-project entry: If the user already has spec files or an existing codebase, read them first. Validate existing artifacts against the expected format, then confirm which phase to start from.

File Organization

Two-layer structure: trunk (current system truth) + changes (incremental work).

text

specs/
├── index.md                    ← navigation hub: all features & recent changes
├── requirements.md             ← project-level requirements (grows incrementally)
├── design.md                   ← system-level architecture (grows incrementally)
├── design-preview/
├── tasks.md                    ← active tasks only
├── status.md
├── spec_<feature_name>.md      ← feature specs (current truth, one per feature)
└── changes/                    ← all incremental work
    ├── FEAT-NNN-name/          ← new feature (full spec lifecycle)
    │   ├── spec.md
    │   ├── design.md
    │   ├── tasks.md
    │   └── delta.md            ← merge instructions for trunk
    ├── CHG-NNN-name/           ← change/enhancement (delta only)
    │   ├── spec.md             ← ADDED / MODIFIED / REMOVED sections
    │   ├── tasks.md
    │   └── delta.md
    └── archive/                ← completed & merged changes

First-time projects: Start with trunk only (no changes/ needed). The changes layer is introduced when the first post-v1 feature or modification begins.

For full lifecycle management details, see Spec Lifecycle Management.

Phase 0 (Optional): Codebase Scan

For existing codebases, run before Phase 1: read dependency files to detect tech stack, list directory tree, identify existing interfaces/models/conventions, and summarize findings.

Output: Write results to specs/status.md under ## Codebase Context (tech stack, key conventions, existing interfaces, directory structure summary). This persists the scan across sessions. Phase 1 references this for requirements scoping; Phase 2a references it for architecture decisions.

Phase 1: Clarify & Scope

Goal: Turn informal requirements into a confirmed, structured requirements.md.

Constraints: Do NOT write any code. Only ask questions and produce documents.

1. Interactive Clarification — Ask user for raw requirements. Summarize goals (3–5 bullets), list ambiguities with options, suggest unconsidered constraints. Iterate until confirmed.
2. Structured Requirements — Produce specs/requirements.md (see template): Background & Objectives, User Roles & Use Cases, Functional Requirements (FR-001...), Non-Functional Requirements, Out of Scope. If Phase 0 ran, populate the "Existing Architecture" section with requirement-relevant context from status.md § Codebase Context.

→ Gate 1: Requirements Review

Per Expert Review Protocol — Gate 1. Exit: User approves (or auto-approved).

Phase 2: Spec

Goal: Produce spec documents that directly drive code generation.

2a: Technical Design → specs/design.md

Based on requirements.md, produce specs/design.md (see template):

1. Architecture overview (tech stack, layers, services)
2. Core module breakdown with responsibilities and dependency directions
3. Key data models, interfaces & interaction flows
4. Cross-cutting concerns (error handling, auth, observability, deployment) — skip on Small track
5. NFR fulfillment matrix + key architecture decisions (ADR format) — skip on Small/Medium track

For existing codebases: populate "Existing Architecture" section with architecture-relevant context from status.md § Codebase Context (what's new vs. modified).

2b: Design Preview → specs/design-preview/

Self-contained HTML prototype visualizing architecture, module layout, UI screens or API flows, and data models.

Constraints:

• Single HTML file per page/screen (inline CSS + JS, no external dependencies) — must open in any browser without a build step.
• Target: validate information architecture and user flow, not pixel-perfect design. Lo-fi is acceptable.
• Limit to ≤ 5 key screens/pages. Prioritize primary user workflow.
• For non-UI projects: Architecture Diagram Preview only (module relationships + data flow as a single HTML page).

UI projects: All generated UI must follow the UI Design Guidelines to avoid AI-template aesthetics.

→ Gate 2: Design Review (2a + 2b combined)

Per Expert Review Protocol — Gate 2. Exit: User approves (or auto-approved).

2c: Task Breakdown → specs/tasks.md

Task table (see template). Target granularity: 30–90 min per task.

2d: Feature Spec → specs/spec_<feature>.md

Per feature (see template): Feature Description & Use Cases, Interface Definition, Data Model, Business Rules & Edge Cases, Test Points (≥ 5 per feature, complex: 10–20; categories: Normal / Error / Boundary / Combination).

→ Gate 3: Implementation Plan Review (2c + 2d combined)

Per Expert Review Protocol — Gate 3. Exit: User approves (or auto-approved).

Spec Quality Checklist

Before leaving Phase 2: every interface has explicit I/O types; every business rule has ≥ 1 test point; specs describe what not how; each spec is self-contained for code generation; edge cases are explicit, not implied.

Phase 3: Generate

Goal: Produce implementation code + tests strictly based on the spec.

Spec adherence — tiered rules:

Tier	Scope	Rule
Strict	Interfaces, data models, business rules	Follow spec exactly. Do not change signatures, field names, or behavior.
Flexible	Internal implementation (function names, code organization, logging, error messages)	AI decides, but must note deviations in Human-review points.
SPEC-GAP	Scenarios the spec doesn't cover (discovered during coding)	Implement a reasonable solution, tag it [SPEC-GAP], and continue. Collect all gaps for batch review in Phase 4.

Never silently deviate from Strict-tier items. If a Strict item is wrong or incomplete, flag it and ask the user — but do not block on every minor gap.

Execution Strategy

1. Order: Sort tasks by dependency graph (topological order). Infrastructure/setup tasks first.
2. Parallelism: Tasks with no mutual dependencies may be executed in parallel (e.g., via subagents). Tasks sharing the same module should be sequential to avoid merge conflicts.
3. Commit cadence: One commit per task, tagged with task ID: feat(TASK-001): ...
4. Failure handling: If a task fails to generate or test correctly after 2 attempts, mark it Blocked in tasks.md, log the reason, and continue with non-dependent tasks. Return to blocked tasks after unblocked tasks complete.
5. Progress tracking: Update tasks.md Status column (Pending → In Progress → Done / Blocked) as each task progresses.

Steps

1. Scan project structure and tech stack (or use Phase 0 results).
2. For each task in tasks.md (per execution strategy above), take its linked spec_xxx.md as input.
3. Output per task:
   • File list (create vs. modify, with paths)
   • Implementation code
   • Tests derived from spec Test Points (TP-001 → test function)
   • Human-review points — Flexible-tier deviations + all [SPEC-GAP] items
4. Add spec traceability comments at module/class level: // SPEC: spec_auth.md | TASK-002 — enables reverse lookup from code to spec.

For existing codebases: clearly distinguish "new file" vs. "modify existing file" and show diffs for modifications.

→ Gate 4: Code Review

Per Expert Review Protocol — Gate 4. Exit: User approves (or auto-approved). Proceed to Phase 4.

Phase 4: Verify

Goal: Confirm generated code satisfies the spec through execution (static compliance is already covered by Gate 4).

4a: Dynamic Verification

Run the following checks in order. Stop and fix if any step fails.

1. Build — Project compiles / bundles without errors.
2. Lint & Type Check — Run linter and type checker (if available). Zero errors required; warnings acceptable.
3. Unit Tests — Execute test suite (pytest, npm test, go test, etc.). Map each TP-ID to pass/fail.
4. Integration Tests — Run integration / E2E tests if defined in tasks.md.
5. Coverage Check — Report test coverage. Flag spec Test Points that have no corresponding test execution.
6. NFR Verification — If requirements.md defines measurable NFRs (response time, throughput), run benchmarks and compare. Log results even if not blocking.
7. Manual Test Checklist — For tasks marked AI-Auto: No in tasks.md, generate a manual test checklist with steps and expected results for the user to execute.

4b: SPEC-GAP Resolution

For each [SPEC-GAP] from Phase 3: Accept (update spec) / Reject (fix code) / Defer (add to backlog).

4c: Implementation Map Update

After all tests pass, update the ## Implementation Map section in each spec_xxx.md with the actual code file paths and function/class names. This enables reverse lookup from spec to code.

Output & Transitions

• Passed — items satisfying the spec; Failed — items deviating (recommend: fix spec or fix code)
• All passed → Phase 5 or next task. Failed → fix in Phase 2 or 3 → re-verify.

Exit condition: All items pass, or user acknowledges remaining gaps.

Workflow completion (initial build): If this is the initial build and no further changes are planned, update status.md: mark all phases complete, remove the Initial Build Progress table, and present a summary to the user (features built, test pass rate, deferred items count).

Phase 5: Evolve — New Features & Changes

Goal: Add new capabilities or modify existing ones while keeping all specs in sync.

Key rule: Always update the spec BEFORE updating the code. Every change goes through specs/changes/.

Step 1: Classify the Work

Type	Criteria	Action
New Feature	Independent business value, new interfaces/models	Create specs/changes/FEAT-NNN-name/, run full Phase 1–4 within it
Change / Enhancement	Modifies existing feature behavior	Create specs/changes/CHG-NNN-name/, write delta spec, run Phase 2d–4
Trivial Fix	Single spec file, single section, no interface/model change	Update trunk spec directly with changelog entry, skip change dir

Step 2: Overlap Check

Before creating the change directory, run Overlap Check against all In-Progress changes listed in specs/index.md. If overlapping Target Specs are found, warn the user and agree on a resolution strategy before proceeding.

Step 3: Work Within the Change Directory

For Features: run the full workflow (Phase 1–4) inside specs/changes/FEAT-NNN/. For Changes: write a delta-format spec.md (ADDED / MODIFIED / REMOVED), then run Phase 2d–4. For Changes that add/remove screens, modify navigation structure, or alter primary interaction patterns (e.g., forms → tables): also run Phase 2b to update design-preview/.

Path rule: All Phase 1–4 outputs go into the change directory, not the trunk. For example, Phase 2a produces specs/changes/FEAT-NNN/design.md, not specs/design.md. The trunk is only updated during Step 4 (Merge to Trunk).

Nesting rule: Changes are always flat — never create a change inside another change directory. If FEAT-NNN's implementation reveals the need for an additional feature, create a sibling FEAT-NNN+1 at the top level (specs/changes/FEAT-NNN+1-name/) and add a dependency note in both tasks.md files.

Apply the same review gates as the main workflow, scoped to the change:

• Interface/architecture change → Gate 2 | Business rule change → Gate 3 | Implementation-only → Gate 4

Step 4: Cross-Feature Impact Analysis

Before generating code, analyze impact across ALL trunk specs:

• Direct: Specs explicitly modified by this change.
• Indirect: Specs that depend on modified interfaces or data models.
• Test: Test points in other specs that may need updating.

Present impact analysis to the user for confirmation.

Step 5: Merge to Trunk

After code is verified (Phase 4 passed):

1. (Features only) Copy changes/FEAT-NNN/spec.md to specs/spec_<feature>.md.
2. Generate delta.md — merge instructions listing every trunk file/section to update.
3. Apply delta to trunk specs (specs/*.md): insert ADDED content, replace MODIFIED sections, remove REMOVED items.
4. Add changelog entries to every modified trunk file.
5. Update specs/index.md with the change reference.
6. Commit all trunk updates atomically: spec: merge FEAT/CHG-NNN to trunk.
7. Move change directory to specs/changes/archive/.

For full lifecycle details, merge rules, and scaling guidance, see Spec Lifecycle Management.

Cross-Phase Guidelines

• No phase skipping: Do not generate code without a confirmed spec. Ask user for confirmation before advancing phases.
• Spec-code traceability: Every code change traces to a spec item (TASK-ID + TP-ID); every spec item has corresponding code and tests.
• Status tracking: Maintain specs/status.md (see template). Update at each phase end with current phase, gate results, and deferred item counts. On session start, read specs/status.md first to restore context.
• Context management: Keep each spec file under ~300 lines. In Phase 3, feed only the relevant spec_xxx.md + related design.md sections — not all spec files at once.
• Expert review: All review gates follow the Expert Review Protocol. Key points: auto-approve when no Critical/Major issues; max 3 rounds per gate; track prior issues across rounds; deferred items logged in spec files. Users can set review preferences in specs/status.md.
• UI de-AI aesthetic: All user-facing UI must follow the UI Design Guidelines to avoid AI-template aesthetics. Gate 2 and Gate 4 reviewers check UI against the de-AI checklist.

Error Recovery

Scenario	Recovery Action
Phase 3: Task fails after 2 attempts	Mark task Blocked in tasks.md, log root cause, continue with non-dependent tasks. After all other tasks complete, revisit blocked tasks — may require spec revision (back to Phase 2d).
Phase 4: Tests fail	Categorize: spec bug (fix spec then re-generate) vs. code bug (fix code, re-run tests). Do not loop more than 3 fix-verify cycles per task — escalate to user.
Phase 4: Test environment unavailable	Generate manual test checklist, document expected setup, and mark verification as Pending-Env in status.md. Proceed with remaining phases that don't require the environment.
SPEC-GAP: Cannot decide autonomously	Tag as [SPEC-GAP-BLOCKED], implement a safe no-op or error response as placeholder, and batch all blocked gaps for user decision before Phase 4 verification.
Phase 5: Delta merge conflict	Follow conflict handling in spec-lifecycle.md. Never force-overwrite trunk — always present both versions to the user.
Cross-session context loss	Read specs/status.md + last completed artifacts (see Session Start). If status.md is missing or stale, scan specs/ directory structure and tasks.md status to reconstruct state.
Phase 1: Requirements deadlock	If the user cannot decide after 3 clarification rounds, present a default recommendation with rationale. Ask for explicit approval or override. Do not loop indefinitely.
Phase 2: Design deadlock	If two design options are equally viable, document both in ADR format (pros/cons/consequences), provide a recommended option, and ask the user to decide. Limit to 2 discussion rounds, then adopt the recommendation if no response.

Templates

For spec file templates, see templates.md (core) and templates-lifecycle.md (lifecycle & review).