Composability Primitives

Gemini CLI's power comes from how its components compose together. There are six primitives that layer on top of each other: GEMINI.md (project context), custom commands (reusable workflows), built-in tools (file ops, shell, search), MCP servers (external tool integrations), extensions (community packages), and agent skills (preview feature for multi-step autonomous workflows). Each layer builds on the ones below it.

1. GEMINI.md Foundation layer — project context, rules, and conventions loaded at session start.
2. Built-in Tools Core capabilities: read_file, write_file, edit, glob, search_file_content, run_shell_command, google_web_search, web_fetch.
3. Custom Commands Reusable .toml-defined slash commands that encode your team's workflows.
4. MCP Servers External tool integrations via the Model Context Protocol — databases, APIs, specialized services.
5. Extensions Community-built packages that bundle tools, commands, and context into installable units.
6. Agent Skills (Preview) Multi-step autonomous workflows that combine all lower layers into high-level capabilities.

The composability model is what makes Gemini CLI more than a chat interface. A single prompt can trigger a custom command that uses built-in tools to read files, calls an MCP server to query a database, references GEMINI.md for project conventions, and produces output formatted according to your team's standards. Each layer is optional — you can be productive with just GEMINI.md and built-in tools. But the more layers you adopt, the more powerful your workflows become.