Software → Software Design
TSD
A technical specification document that defines concrete implementation contracts, technology choices, schemas, interfaces, testing expectations, and deployment details.
Motivation
A TSD turns an approved design into implementation-level agreements. It gives developers, reviewers, QA, platform teams, and operators a precise reference for how a change will be built and verified.
Typical contents
- Selected technologies and libraries
- Detailed component behavior
- API contracts and endpoint rules
- Data schemas, migrations, and validation
- Error handling and failure behavior
- Security and performance requirements
- Test strategy and acceptance mapping
- Deployment, configuration, observability, and rollback plans
Relationship to the SDD
The SDD explains the system design and major boundaries. The TSD provides the concrete choices and contracts needed to implement that design. Small changes may combine both concerns in one document; large programs often separate them for clarity.
Common mistakes
- Specifying tools without explaining why they satisfy the design constraints.
- Leaving failure, migration, monitoring, or rollback behavior undefined.
- Making the document so detailed that normal implementation changes require constant rewriting.
- Treating the specification as a replacement for communication and code review.