Spec Format

Spec Format

This skill covers how to write and structure SDD specifications.

Spec File Structure

Canonical specs (post-finish) live under the configured canonical spec root (.ae-config.json specRoot, default docs/specs). Discover canonical spec paths with ae sdd spec list (no flag by default).

Change-set specs for a given change set live under changes/<name>/specs/ and may be nested by domain/subdomain.

docs/specs/
  <domain>/
    <subdomain>/
      <capability>.md

Capability Spec Format

Each capability spec follows this structure:

# <Capability Name>

## Overview

Brief description of what this capability does and why it exists.

## Access (optional)

Include this section only when access constraints are meaningful for the capability.

> Authenticated

or

> Public

Projects define their own access levels in a platform-level spec (e.g., `auth-gating.md`).

## Dependencies (optional)

Optional section listing dependencies on other specs or external systems.

## Requirements

Requirements as a bulleted list. Optional grouping headings (### Group Name) for organization.

### <Optional Group>

- The system SHALL <requirement in active voice>.
- WHEN <trigger> the system SHALL <action>.

### <Another Group>

- WHILE <state> the system SHALL <action>.

Topic headings (groups)

Under ## Requirements, group headings are simply whatever the next heading level down is:

• In kind: new specs, groups/topics are typically ### <Topic>
• In kind: delta specs, groups/topics live under ### ADDED/MODIFIED/REMOVED, so topics are #### <Topic>

Entry and Exit are just common topic names for user-facing or system-facing flows (they are not special section types).

Example (new spec):

## Requirements

### Entry

- WHEN a user navigates to <destination> the system SHALL <action>.

### Exit

- WHEN <action> completes the system SHALL redirect to <destination>.

Surface-Agnostic Language

Use action-oriented but surface-agnostic language in Entry/Exit:

The spec describes what the user intends to do, not how they physically do it.

EARS Syntax

Requirements use EARS (Easy Approach to Requirements Syntax) patterns. Clauses always appear in the same order: WHILE <state>, WHEN <trigger>, then the system SHALL <response>. Omit clauses you do not need.

Pattern selection guide

• Start with the scope: if it is always true, use Ubiquitous.
• If a sustained condition limits the behavior, use State-driven.
• If a discrete event triggers the behavior, use Event-driven.
• If both a state and a trigger apply, use Complex (WHILE + WHEN).
• If you are describing error handling, use Unwanted behavior instead of nesting IF inside WHEN.
• If behavior only applies when a feature is included, use Optional feature.

Examples

• The system SHALL validate all user input before processing.
• WHEN the user submits the form the system SHALL save the data.
• WHILE in maintenance mode the system SHALL reject new connections.
• IF the database connection fails THEN the system SHALL retry with exponential backoff.
• WHERE two-factor auth is enabled the system SHALL require a verification code.
• WHILE the user is authenticated, WHEN a session expires the system SHALL prompt for re-authentication.

Change Set Specs (changes/<name>/specs/)

All change set specs live in changes/<name>/specs/ and MUST include YAML frontmatter:

Validation (required)

After you write or edit any change-set spec under changes/<name>/specs/**/*.md, you MUST run the validator command against the exact file you changed.

• Run: ae sdd spec validate --path <change-spec-path>

If validation fails:

• You MUST fix the spec content.
• You MUST re-run the validator.
• Repeat until it prints OK.

---
kind: new | delta
---

Optional frontmatter fields

Change-set specs MAY include additional YAML frontmatter fields when helpful. This is intentionally extensible for future tooling.

depends_on (optional)

Use depends_on to express spec-to-spec dependencies in a machine-readable form:

---
kind: new
depends_on:
  - docs/specs/<domain>/<...>/<capability>.md
---

Prefer using canonical paths returned by ae sdd spec list even when the dependency is being modified in the current change set.

kind: new

Use kind: new when the spec does not exist in canonical yet. Write it like a normal spec. Do NOT use delta markers or delta sections.

kind: delta

Use kind: delta when the spec modifies an existing canonical spec.

kind: delta specs use section buckets (NOT blockquote markers):

• ### ADDED
• ### MODIFIED
• ### REMOVED

Under each bucket, use #### <Topic> headings.

For MODIFIED topics, requirements MUST be represented as adjacent Before/After blocks:

### MODIFIED

#### <Topic>

**Before:**
- The system SHALL <old text>.

**After:**
- The system SHALL <new text>.

For ADDED topics:

### ADDED

#### <Topic>

- The system SHALL <new requirement>.

For REMOVED topics:

### REMOVED

#### <Topic>

- The system SHALL <requirement being removed>.

**Reason:** <Why this requirement is being removed>

Where ADDED/MODIFIED/REMOVED may appear

Only use ### ADDED/MODIFIED/REMOVED inside ## Requirements and ## Access (if ## Access is present).

• ## Access is optional; omit it for foundational/mechanism specs (e.g., navigation, rate limiting).
• When ## Access is present in a delta spec, do not add #### topics under it; put the Before/After or bullets directly under the corresponding ### bucket.

RFC 2119 Keywords

Requirements use RFC 2119 language:

• SHALL - Absolute requirement
• SHALL NOT - Absolute prohibition
• SHOULD - Recommended but not required
• SHOULD NOT - Discouraged but not prohibited
• MAY - Optional

Prefer SHALL for most requirements. Use SHOULD/MAY sparingly when behavior is recommended or optional. Do not use SHALL to avoid choosing the right EARS pattern.

Writing Good Requirements

1. One requirement per bullet - Don't combine multiple requirements
2. Active voice - "The system SHALL validate" not "Validation shall be performed"
3. Testable - Requirements should be verifiable
4. Implementation-agnostic - Describe WHAT, not HOW
5. No ambiguity - Avoid words like "appropriate", "reasonable", "user-friendly"
6. Use EARS patterns - Pick the appropriate pattern for the requirement type

Referencing Requirements

Tasks, plans, and reconciliation reference requirements by quoting the exact EARS line from the spec.

Example in tasks.md:

**Requirements:**
- "WHEN the user submits the form the system SHALL save the form data."
- "IF validation fails THEN the system SHALL display error messages."

Flat vs Grouped Delta Specs

Flat: One delta file per modified capability (default)

changes/<name>/specs/auth/login.md
changes/<name>/specs/auth/logout.md

Grouped: Multiple related changes in one file (for tightly coupled changes)

changes/<name>/specs/auth/session-management.md  # covers login + logout + refresh

Use grouped only when changes are truly interdependent and reviewing separately would lose context.