Tech Design Generation Skill

What Is a Technical Design Document?

A Technical Design Document (TDD) is the engineering blueprint that translates product requirements into a concrete, implementable architecture. It sits between the Software Requirements Specification (SRS) and the actual code, serving as the contract between the engineering team and the rest of the organization about how a system will be built. A well-crafted TDD reduces implementation risk, surfaces architectural trade-offs early, and provides a lasting record of why specific technical decisions were made.

The Google Design Doc tradition emphasizes that design documents are not just about documenting a decision after the fact -- they are a tool for thinking through a problem rigorously before committing to code. The RFC (Request for Comments) tradition adds the dimension of structured peer review, ensuring that designs benefit from collective expertise. Uber and Meta engineering standards contribute a focus on scalability, operational readiness, and production-grade thinking from day one.

This skill combines all three traditions. Every generated Technical Design Document presents at least two alternative solutions, evaluates them against explicit criteria, and documents the rationale behind the chosen approach. The document covers architecture, API design, data modeling, security, performance, observability, and deployment -- everything an engineering team needs to move from design to implementation with confidence.

Seven-Step Workflow

Every Technical Design Document generated by this skill follows a disciplined seven-step process. Each step must be completed before moving to the next.

Sub-agent boundary: Steps 1-3 are performed by the orchestrator (commands/tech-design.md) in the main context. Steps 4-7 are performed by a generation sub-agent (Task(subagent_type="general-purpose")) that reads references/generation-instructions.md, references/template.md, and references/checklist.md directly. The sub-agent operates in an isolated context and receives a structured prompt with all Step 1-3 outputs.

Step 1 -- Deep Scan Codebase

Before writing anything, perform a thorough scan of the current project to build deep technical understanding.