Spec File Conventions

Conventions for writing implementation-ready specification documents that serve as the single source of truth for feature design and implementation.

Spec Files vs Documentation Files

Projects often maintain two distinct documentation layers. Understand the distinction to keep each layer focused.

Spec Files

• •Purpose: Single source of truth for design and implementation decisions
• •Audience: Implementors and reviewers
• •Content: Full design details — schemas, field definitions, decision rationale, implementation notes
• •Lifecycle: Created before implementation, updated progressively during implementation
• •Self-contained: A reader should understand the full design without opening other files

Documentation Files

• •Purpose: Quick-reference guides after implementation
• •Audience: Developers using the feature
• •Content: Usage-focused ("how to use"), not "how it was designed"
• •Brevity: Avoid duplicating definitions — point to source files (.sql, .proto, .rb, config files)
• •No historical context: Omit decision rationale and alternatives considered

When a spec lists documentation files as deliverables, verify their scope is clear. The spec itself must contain enough inline detail to be self-contained — never defer design details to documentation files.

Spec File Structure

A well-structured spec includes:

1. •Title and overview — what the feature does and why it's needed
2. •Data model — include full DDL or schema definitions, not just prose descriptions
3. •Architecture — name concrete classes/modules; specify where each piece of logic lives
4. •Behavior — cover the happy path end-to-end, then every error condition and edge case
5. •Integration — specify which existing modules are touched and how
6. •Security considerations — credential handling, rate limiting, audit logging, sensitive data
7. •Operations — setup steps, cleanup/purge strategies, key rotation procedures
8. •Scope — explicitly state what's in and out; note dependencies on future work
9. •Deliverables — enumerate every file to create or modify
10. •Current Status — interview or implementation progress (see below)

Self-Containment Principle

Inline all design details directly in the spec:

• •Full schema definitions (SQL DDL, protobuf, JSON schemas, etc.)
• •Field-level tables with types, constraints, and descriptions
• •Decision rationale for non-obvious choices
• •Error handling behavior for each failure mode

A reader should never need to open another file to understand the complete design.

Resolving TODOs

Before a spec is considered interview-complete:

• •Every TODO must be resolved
• •TODOs representing open design questions must be resolved through discussion; inline the decision and rationale directly
• •TODOs representing implementation tasks should be reworded as clear action items in the deliverables or checklist
• •Grep the spec for ambiguous language: "TBD", "maybe", "possibly", "to be decided"

Current Status Section

Every spec must end with a "Current Status" section. Its format differs by phase. See references/current-status-format.md for detailed examples across interview and implementation phases.

During Interview

Keep concise — list covered areas with key decisions and remaining areas with rough question count:

## Current Status

Interview in progress.

Covered:
- Data Model: field types finalized, indexes decided
- Architecture: service object pattern chosen

Remaining (~8 questions):
- Behavior & Logic: error handling details
- Security: rate limiting defaults
- Operations: cleanup strategy

After Interview / During Implementation

Expand into a checklist and updates format:

## Current Status

Implementation in progress. Implementors MUST keep this section updated as they work.

### Checklist
- [ ] Create database migration
- [ ] Implement service object
- [ ] Add request specs
- [ ] Write documentation

### Updates

- YYYY-MM-DD: Migration created, model specs passing
- YYYY-MM-DD: Service object implemented with error handling

Additional Resources

Reference Files

• •references/current-status-format.md — Detailed examples of Current Status sections across interview and implementation phases