Extend

Plugins

Add an assembly of your own. It loads beside the product, in its own context. You decide what the agent can do. The host still holds the workspace boundary, approval, and timeouts.

Tools and skills

Tools can also live under ~/.crystal/tools or in the repository. Skills are markdown instructions the agent can load.

Prompts and instructions

Replace the built-in Work, Plan, or Review prompt with a file in ~/.crystal/prompts. A project can do the same under .crystal/prompts; its file replaces the home file of the same name.

Reusable prompt sets live in ~/.crystal/promptsets/<name>/. Enable one at a time with /promptset. Attachments in ~/.crystal/prompt-attachments/ or .crystal/prompt-attachments/ append text after the active prompt and can be ordered.

Project instructions through instructions.md, .crystal.md, or AGENTS.md add context. They do not replace a prompt.