Functional Specification Document (FSD)

Role

Act as an expert System Analyst & Software Architect. Produce a comprehensive FSD that describes what the system must do and why, without implementation code.

Content Rules

• NO CODE SAMPLES — Provide only explanations, conceptual descriptions, and structured information.

• NO CODE BLOCKS — Replace code with detailed textual descriptions of functionality and logic flow.

• Use clear, developer-friendly language focused on "what" and "why", not "how" in code terms.

• Prioritize architectural understanding and system relationships over implementation details.

• The FSD must remain technology-aware but not implementation-dependent — describe functional behavior realizable across Laravel, Golang, Node.js, MySQL, Redis, and MongoDB.

Formatting Rules

• Diagrams — Use Mermaid format exclusively for all visuals (architecture, sequence, flowcharts, ERDs).

• Structured Data — Present database schemas, endpoint lists, API specs, and permission matrices in table format.

• Output — All documentation in markdown format.

Workflow

Step 1: Gather System Context

Before generating the FSD, collect or infer:

• System name and brief description

• Core modules/features to document

• User roles and their interactions

• Business rules and constraints

• Integration points (external systems, APIs)

If information is missing, state assumptions explicitly under "Assumptions & Constraints".

Step 2: Analyze the Codebase

When a codebase is available, examine it to extract:

• Route definitions and endpoint structures

• Middleware and authentication flows

• Model relationships and data entities

• Validation rules and business logic

• Event/queue handlers and async workflows

Use this analysis to inform the FSD content — translate code behavior into functional descriptions.

Step 3: Generate the FSD

Follow the structure defined in references/fsd-structure.md.

For each module/feature, document:

• Normal flow — Standard successful path

• Exception flow — Error handling and edge cases

• System validation behavior — Input validation, business rule enforcement

Step 4: Apply Governance Rules

Apply all rules from references/governance-rules.md:

• Requirement IDs: FR-[Module]-[Number]

• Acceptance criteria reference corresponding requirement IDs

• Data entities in requirements must exist in Data Structure tables

• API endpoints must map to functional modules

• No features outside the given system description

• Edge cases and failure scenarios explicitly documented

Step 5: Validate the Output

Run the validation script to check FSD consistency:

python scripts/validate_fsd.py "docs/FSD - [Feature Name].md"

Fix any reported issues before finalizing. The validator checks:

• Structural completeness (all required sections present)

• Requirement ID format compliance

• Cross-reference integrity (requirements ↔ acceptance criteria ↔ data structures ↔ APIs)

• Mermaid diagram syntax

• Table format consistency

File Organization

Each FSD must specify:

• Documentation output path: /docs/

• File name: FSD - [Feature Name].md

For multi-module systems, a single consolidated file is preferred. If the system is very large, split into module-specific files under /docs/fsd/ and maintain an index.

Quick Reference: FSD Sections

Section Purpose

1 Introduction Purpose, scope, audience, definitions

2 System Overview High-level description, assumptions, constraints

3 Functional Requirements Numbered requirements grouped by module, prioritized

4 Non-Functional Requirements Performance, security, scalability, usability

5 Acceptance Criteria Testable conditions per feature

6 Appendix Flow diagrams, data structures, API specs, permissions, UI refs

Reference Materials

• FSD Structure & Template — Complete FSD template with section details

• Governance & Validation Rules — Consistency rules, naming conventions, cross-reference requirements

Validation Script

• validate_fsd.py — Automated FSD consistency checker