singularity-forge/docs/dev/extending-pi/01-what-are-extensions.md

What Are Extensions?

Extensions are TypeScript modules that hook into pi's runtime to extend its behavior. They can:

• Register custom tools the LLM can call (via pi.registerTool())
• Intercept and modify events — block dangerous tool calls, transform user input, inject context
• Register slash commands (/mycommand) for the user
• Render custom UI — dialogs, selectors, games, overlays, custom editors
• Persist state across session restarts
• Control how tool calls and messages appear in the TUI
• Modify the system prompt dynamically per-turn
• Manage models and providers — register custom providers, switch models
• Override built-in tools — wrap read, bash, edit, write with custom logic

Why this matters: Extensions are the primary mechanism for customizing pi. They turn pi from a generic coding agent into your coding agent — with your guardrails, your tools, your workflow.

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