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Writing Specs

How to write effective specifications that produce good code. Specs are the foundation of the entire workflow — bad specs lead to bad code, no matter how good the AI is.

Spec Structure​

Every spec file at openspec/specs/{domain}/spec.md follows this structure:

# <Capability Name> Specification

**Status**: idea | planned | in-progress | done
**Scope**: company-wide | {app-name}
**OpenSpec changes**:
- [change-name](../../changes/change-name/)
- [archived-change](../../changes/archive/YYYY-MM-DD-archived-change/) _(archived YYYY-MM-DD)_

## Purpose
<What this capability does and why it exists (2–5 sentences). Include relevant ADR references.>

## Requirements

### REQ-{NNN}: <Name>
<Description using RFC 2119 keywords>

#### Scenario: <Name>
- GIVEN <precondition>
- WHEN <action>
- THEN <expected result>
- AND <additional result>

## Non-Functional Requirements

- **Performance:** <measurable performance requirement>
- **Accessibility:** <WCAG or usability requirement>
- **Internationalization:** Dutch and English MUST be supported (ADR-005)

## Acceptance Criteria

- [ ] <testable criterion>

## Notes

<Open questions, constraints, dependencies, related ADRs.>

Field reference​

FieldRequiredNotes
**Status**Yesidea → planned → in-progress → done
**Scope**Yescompany-wide (in hydra/openspec/specs/) or app name (in {app}/openspec/specs/)
**OpenSpec changes**YesVertical list, one entry per line, oldest first. _(none yet)_ until first change created. Archived entries include _(archived YYYY-MM-DD)_. See Grouping rule below.
## Non-Functional RequirementsYesAlways present, even if minimal
## Acceptance CriteriaYesPlaceholder OK for idea status; fill in before moving to planned
## NotesYesAlways present

Status lifecycle​

idea ──► planned ──► in-progress ──► done
  │          │                         │
  │     ready for /opsx-ff             │ new change created
  │                                    ▼
still fuzzy, fill in             in-progress (again)
Acceptance Criteria first
StatusMeaning
ideaConcept noted — Purpose defined, Requirements fuzzy
plannedAcceptance criteria fully defined — ready for /opsx-ff
in-progressOne or more OpenSpec changes have been created from this spec
doneAll associated OpenSpec changes have been archived

Re-opening a done spec: If a new change is created that modifies a done spec, set the status back to in-progress. The **OpenSpec changes** list preserves the full history (archived entries stay visible).

OpenSpec changes list format​

List entries oldest-first (top = oldest, bottom = newest). One entry per line:

**OpenSpec changes**:
- [change-name](../../changes/change-name/)
- [archived-change](../../changes/archive/YYYY-MM-DD-name/) _(archived YYYY-MM-DD)_

When the list exceeds 15 entries, group multiple changes per bullet by timeframe (same day → same month → same year). Oldest group first. Never remove entries.

**OpenSpec changes**:
- [change-a](link/), [change-b](link/) _(Jan 2026)_
- [change-c](link/), [change-d](link/) _(Mar 2026)_
- [newest-change](link/) _(Apr 2026)_

Group at the coarsest level that keeps the list under 15 bullets while preserving order. Start by grouping same-day entries, then same-month, then same-year if still too long.

RFC 2119 Keywords​

Use these keywords deliberately to communicate the importance of each requirement:

KeywordMeaningUse when
MUST / SHALLAbsolute requirement. Non-negotiable.The feature won't work correctly without this
MUST NOT / SHALL NOTAbsolute prohibitionDoing this would break something or violate a constraint
SHOULDRecommended, but exceptions may existBest practice that can be skipped with justification
SHOULD NOTDiscouraged, but exceptions may existNot ideal but acceptable in some cases
MAYOptionalNice to have, up to implementer

Examples​

# Good — clear intention
The API endpoint MUST return HTTP 404 when the resource does not exist.
The response SHOULD include a human-readable error message.
The response MAY include a machine-readable error code.

# Bad — vague, no keywords
The API should handle errors properly.

Rule of thumb: Prefer MUST/SHALL for normative requirements — if behavior is genuinely required, say so. Use SHOULD when real exceptions are acceptable. Reserve MAY for truly optional behavior; if it can be expressed as MUST or SHOULD, prefer that instead.

Writing Scenarios​

Scenarios use the Gherkin format (GIVEN/WHEN/THEN) to describe specific behaviors. They serve as both documentation and acceptance criteria for implementation.

CRITICAL: Scenario headings MUST use exactly 4 hashtags (####), not 3. Using ### instead of ####, or bullet points, will fail silently — the spec parser won't recognize them as scenarios.

Good Scenarios​

#### Scenario: Successful login with valid credentials
- GIVEN a user with email "test@example.com" and a valid password
- WHEN they submit the login form
- THEN the system MUST return a JWT token
- AND the user MUST be redirected to the dashboard
- AND the session MUST be stored in the database

#### Scenario: Login fails with invalid password
- GIVEN a user with email "test@example.com"
- WHEN they submit the login form with an incorrect password
- THEN the system MUST return HTTP 401
- AND the response body MUST contain `{"error": "Invalid credentials"}`
- AND the failed attempt MUST be logged

Bad Scenarios​

# Too vague
#### Scenario: Login works
- GIVEN a user
- WHEN they log in
- THEN it works

# Too implementation-specific
#### Scenario: Login
- GIVEN a POST to /api/v1/auth/login with body {"email":"x","pass":"y"}
- WHEN AuthController::login() calls UserService::authenticate()
- THEN it calls $mapper->findByEmail() and JWTService::generate()

Tips for Good Scenarios​

  1. Cover the happy path first, then error cases, then edge cases
  2. Be specific about inputs and outputs — what data, what status codes, what format
  3. Focus on behavior, not implementation — describe what happens, not which classes/methods do it
  4. One scenario, one behavior — don't combine multiple behaviors in one scenario
  5. Include negative scenarios — what happens when things go wrong?

Delta Specs​

When making changes to existing functionality, use delta specs to show what's changing.

ADDED​

New requirements that didn't exist before:

## ADDED Requirements

### REQ-001: Full-Text Search
The system MUST support full-text search across publication titles and content bodies using PostgreSQL's tsvector.

#### Scenario: Search returns matching publications
- GIVEN publications with titles "Climate Report 2024" and "Budget Overview"
- WHEN a user searches for "climate"
- THEN the results MUST include "Climate Report 2024"
- AND the results MUST NOT include "Budget Overview"
- AND results MUST be ordered by relevance score

MODIFIED​

Changes to existing requirements. Always note what the previous behavior was:

## MODIFIED Requirements

### REQ-003: Session Duration
The system MUST expire user sessions after 15 minutes of inactivity.

(Previously: sessions expired after 30 minutes of inactivity)

#### Scenario: Session expires
- GIVEN a user who has been inactive for 16 minutes
- WHEN they make a request
- THEN the system MUST return HTTP 401
- AND the session MUST be cleared from the database

REMOVED​

Requirements being deprecated. Always explain why:

## REMOVED Requirements

### REQ-002: Remember Me Checkbox
(Deprecated: replaced by automatic session refresh on activity. Removing the checkbox simplifies the login form and improves security by eliminating long-lived sessions.)

RENAMED​

Requirements whose name is changing but whose behavior is unchanged. Always use FROM:/TO: format so reviewers can track the rename:

## RENAMED Requirements

### REQ-004: Old Requirement Name
FROM: Old Requirement Name
TO: New Requirement Name
<!-- No behavior change — rename only -->

Referencing Shared Specs​

When your requirement relates to a cross-project convention, reference the shared spec:

### REQ-005: Publication API Endpoint
The system MUST provide a REST endpoint at `/index.php/apps/opencatalogi/api/publications`.

See shared spec: `api-patterns/spec.md#requirement-url-structure` for URL conventions.
See shared spec: `api-patterns/spec.md#requirement-cors-support` for CORS requirements.

Shared specs live in hydra/openspec/specs/ (company-wide, maintained by Conduction). Check that directory for currently available shared specs — the list evolves as new cross-app specs are added. Company-wide architectural decisions (NL Design System, API conventions, security, i18n) are captured in ADRs under hydra/openspec/architecture/.

Cross-Referencing Requirements​

REQ-NNN numbers are unique only within their own spec file. When referring to a requirement from outside its spec — in tasks.md, PR titles, GitHub issues, or other spec files — always prefix with the capability name:

{capability-name}#REQ-NNN

Examples:

ContextFormatExample
tasks.md task entry{capability}#REQ-NNN — {title}archival-destruction-workflow#REQ-009 — Advance Archivist Notifications
Cross-spec reference[capability/spec.md#req-nnn](../capability/spec.md#req-nnn)[archival-destruction-workflow#REQ-006](../archival-destruction-workflow/spec.md#req-006-legal-hold-management)
PR title / issue{capability}#REQ-NNNarchival-destruction-workflow#REQ-003
@spec PHPDoc tagopenspec/changes/{change}/tasks.md#task-N(points to tasks.md, not directly to REQ)

Inside the spec file itself, bare REQ-NNN is sufficient — the file location already provides the namespace.

Organizing Specs​

By domain capability​

openspec/specs/
├── auth/spec.md            # Authentication & sessions
├── publications/spec.md    # Publication CRUD
├── search/spec.md          # Search functionality
├── export/spec.md          # Data export features
└── notifications/spec.md   # User notifications

Tips​

  • One capability per spec file — don't mix unrelated concerns
  • Name directories for the domain concept, not the implementation (search/, not search-controller/)
  • Keep specs focused — if a spec file grows past ~100 requirements, split it
  • Update specs when behavior changes — specs must always reflect the current system behavior

Common Mistakes​

1. Writing specs after code​

Specs written after implementation just document what exists. They don't help you think through requirements or catch issues early. Write specs first.

2. Being too vague​

# Bad
The system should handle errors.

# Good
The system MUST return HTTP 400 with a JSON body containing an `error` field
when the request body fails validation.

3. Being too implementation-specific​

# Bad — tied to specific classes
The AuthController MUST call UserMapper::findByEmail().

# Good — describes behavior
The system MUST look up users by email address during authentication.

4. Missing error scenarios​

Always consider: what happens when the input is invalid? When the resource doesn't exist? When the user isn't authorized? When an external service is down?

5. Using MUST for everything​

If everything is MUST, nothing is distinguishable. Reserve MUST for true requirements and use SHOULD/MAY for less critical behaviors.

6. Writing untestable requirements​

# Bad — how do you verify this?
The system MUST be fast.

# Good — measurable
The search endpoint MUST respond within 500ms for queries returning fewer than 100 results.

Task Breakdown​

When writing tasks.md, each task should:

  1. Be completable in one focused iteration (15-30 minutes)
  2. Have a clear spec_ref pointing to the specific requirement
  3. List files to scope the work
  4. Include acceptance_criteria extracted from spec scenarios
  5. Be ordered by dependency — foundations first, features second, polish third

Mandatory deliverables per feature​

Every feature implemented from a spec MUST include all three layers:

  1. Backend logic — service/controller code that implements the requirement
  2. UI — a user-facing interface so the feature is actually usable (Vue component, page, dialog, form, etc.)
  3. Tests — covering both backend and frontend:
    • Unit tests (PHPUnit) for services, mappers, and business logic
    • Newman/Postman tests for API endpoints (add to the app's Postman collection)
    • Browser tests (Playwright MCP) for the UI — verify the feature works end-to-end through the browser

After implementing each task, the agent MUST run the relevant tests to confirm everything works:

  • composer test or vendor/bin/phpunit for unit tests
  • newman run for API tests
  • Browser MCP snapshot/interaction for UI verification

A task is NOT complete until its tests pass.

Good task breakdown​

### Task 1: Create SearchService with basic query method
- **spec_ref**: `openspec/specs/search/spec.md#requirement-full-text-search`
- **files**: `lib/Service/SearchService.php`
- **acceptance_criteria**:
  - GIVEN a search query WHEN SearchService::search("test") is called THEN it returns matching objects
- [ ] Implement service logic
- [ ] Write unit test (`tests/Unit/Service/SearchServiceTest.php`)
- [ ] Run unit tests — confirm passing

### Task 2: Create SearchController with GET endpoint
- **spec_ref**: `openspec/specs/search/spec.md#requirement-search-api-endpoint`
- **files**: `lib/Controller/SearchController.php`, `appinfo/routes.php`
- **acceptance_criteria**:
  - GIVEN a GET request to /api/search?q=test THEN returns JSON array of results
- [ ] Implement controller and route
- [ ] Add Newman/Postman test to collection
- [ ] Run Newman tests — confirm passing

### Task 3: Add search UI page
- **spec_ref**: `openspec/specs/search/spec.md#requirement-search-ui`
- **files**: `src/views/SearchView.vue`, `src/router/index.js`
- **acceptance_criteria**:
  - GIVEN a user navigating to the search page WHEN they enter a query THEN results are displayed
- [ ] Implement Vue component
- [ ] Build frontend (`npm run build`)
- [ ] Browser test — navigate to page, enter query, verify results appear

### Task 4: Add pagination to search results
- **spec_ref**: `openspec/specs/search/spec.md#requirement-search-pagination`
- **files**: `lib/Service/SearchService.php`, `lib/Controller/SearchController.php`, `src/views/SearchView.vue`
- **acceptance_criteria**:
  - GIVEN 50 results WHEN requesting page=2&limit=10 THEN returns results 11-20 with total count
- [ ] Implement backend pagination
- [ ] Update UI with pagination controls
- [ ] Add Newman test for pagination params
- [ ] Run all tests — confirm passing

Bad task breakdown​

### Task 1: Implement search
- [ ] Do everything

### Task 2: (also bad) Backend only, no UI or tests
- [ ] Add SearchService
- [ ] Add SearchController
# Missing: no UI (users can't use it), no tests (nothing verified)