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Specification
The foundational reference for all downstream technical work
Definition
A specification is a formal document that defines the requirements, constraints, interfaces, and expected behaviors of a system, protocol, or component. It serves as the authoritative source of truth from which all other technical documentation and implementation work derives.
Unlike implementation-focused documentation, a specification describes what a system must do and the boundaries within which it must operate—rather than how it currently does something. This distinction is critical: implementations can change, but the specification defines the contract.
Core Components
A well-formed specification typically includes:
- Requirements: Mandatory behaviors and capabilities the system must exhibit
- Constraints: Boundaries, limitations, and invariants that must be preserved
- Interfaces: The contracts between components, including data formats, protocols, and APIs
- Behaviors: Expected responses to inputs, state transitions, and edge cases
- Definitions: Precise terminology to eliminate ambiguity
Why Specifications Matter
Without a specification, technical work becomes anchored to implementation details. This creates several problems:
- Documentation drift: When docs describe “how things work” rather than “how things should work,” they become stale the moment code changes
- Inconsistent implementations: Multiple teams implementing the same system may make incompatible choices
- Untestable claims: Without defined requirements, there’s no objective basis for determining correctness
- Knowledge silos: Understanding lives in people’s heads rather than in shared artifacts
Relationship to Downstream Work
Every document type in the technical documentation ecosystem traces its authority back to the specification:
- Implementation docs translate spec requirements into working systems
- Integration docs explain how to connect with spec-defined interfaces
- Consumer docs teach users to work within spec-defined behaviors
- Validation docs verify that implementations match spec requirements
- Community docs propose changes to the spec or track its evolution
The specification doesn’t contain all knowledge—but it contains the canonical knowledge from which everything else flows.
Characteristics of Good Specifications
- Precise: Uses unambiguous language; defines terms explicitly
- Complete: Covers all required behaviors; acknowledges areas left unspecified
- Testable: Every requirement can be verified through observation
- Stable: Changes infrequently and through deliberate process
- Versioned: Tracks evolution over time with clear compatibility semantics