danielfortizv/sdd-comparative-study/spec-writer

Spec Writer

Create and maintain .spec.md files that capture functional requirements and link to their verification tests.

When to use

• After requirement-gathering produces confirmed requirements
• When existing specs need updating due to changed requirements
• When implementation revealed gaps that need documenting

Steps

1. Determine scope. Decide whether to create a new spec or update an existing one. One spec per logical unit of functionality — don't combine unrelated features.

1. Write frontmatter. Every spec requires YAML frontmatter:

```yaml

name: Feature Name description: Brief description of what this spec covers targets:

• ../src/path/to/implementation.py
• ../src/path/to/related/**/*.py

```

• name: Human-readable feature name
• description: One-line summary
• targets: Relative paths or glob patterns to implementation files. At least one required.

1. Document requirements. Write clear, scannable requirements:

• Start with an API contract code block if there's a public interface
• Use headings to organize by feature area
• Be specific about expected behavior and edge cases
• Describe error handling expectations

1. Link tests. Add [@test] links inline, next to the requirements they verify:

```markdown

• Invalid passwords return 401

[@test] ../tests/test_auth_invalid_password.py ```

1. Review against styleguide. Check the spec against the Spec Styleguide: concise, scannable, context around test links, clear headings, specific about behavior, granular test files.

1. Save the spec. Place spec files in the project's specs/ directory with a .spec.md extension.

Complete example

---
name: Shopping Cart
description: Add, remove, and checkout operations for the shopping cart
targets:
  -../src/cart.py
  -../src/checkout.py
---
 
# Shopping Cart
 
## Core operations
 

def add_item(cart_id: str, product_id: str, quantity: int) -> Cart: ... def remove_item(cart_id: str, product_id: str) -> Cart: ... def checkout(cart_id: str, payment_method: str) -> Order: ...

 
`[@test] ../tests/cart/test_cart_operations.py`
 
## Quantity rules
 
- Quantity must be >= 1; values <= 0 raise `ValueError`
  `[@test] ../tests/cart/test_quantity_validation.py`
- Adding an existing item increments quantity instead of duplicating
  `[@test] ../tests/cart/test_add_existing_item.py`
 
## Checkout
 
- Empty cart raises `CheckoutError`
  `[@test] ../tests/cart/test_empty_checkout.py`
- Out-of-stock items are removed and the user is notified
  `[@test] ../tests/cart/test_stock_check.py`

Spec format reference

See Spec Format for the complete format specification.