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Codebase design skill

Codebase design is part of Matt Pocock's engineering skills. Its job is to give the agent a shared vocabulary for deep modules, seams and interfaces. It loads on its own when a request matches its description, and you can also call it by name.

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When the agent reaches for it

The agent keeps every installed skill's description in view and loads the full instructions when a request matches. This is the description it reads:

Shared vocabulary for designing deep modules. Use when the user wants to design or improve a module's interface, find deepening opportunities, decide where a seam goes, make code more testable or AI-navigable, or when another skill needs the deep-module vocabulary.

What the instructions cover

The sections of its SKILL.md, in order.

  • Glossary
  • Deep vs shallow
  • Principles
  • Designing for testability
  • Relationships
  • Rejected framings
  • Going deeper

What ships with it

Besides SKILL.md, the folder carries these. The agent opens them only when a step in the instructions calls for one.

  • agents/ 1 file · 102 B
  • DEEPENING.md 2 KB
  • DESIGN-IT-TWICE.md 3 KB

Install the codebase design skill

In Claude Code, run this in a session. It comes from the publisher's own instructions.

Claude Code 
/plugin install mattpocock-skills

License: MIT.

In Longwave, add Engineering Skills from the marketplace. It installs all 37 of its skills, and your Claude Code, Codex and OpenCode threads can use them.

Questions people ask

How do I install the codebase design skill?

In Claude Code, run /plugin install mattpocock-skills. In Longwave, add Engineering Skills from the marketplace, and its skills reach your Claude Code, Codex and OpenCode threads.

When does the agent use the codebase design skill?

When a request matches its description. The agent keeps only the name and description of each installed skill in view, and reads the full instructions when a task fits. You can also ask for it by name.

Use your skills in every harness.

Longwave installs a skill collection once, and your Claude Code, Codex and OpenCode threads can all use it.

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