gemini-cli/docs/architecture.md

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# Gemini CLI Architecture Overview
This document provides a high-level overview of the Gemini CLI's architecture. Understanding the main components and their interactions can be helpful for both users and developers.
## Core Components
The Gemini CLI is primarily composed of two main packages, along with a suite of tools that the system utilizes:
1. **CLI Package (`packages/cli`):**
- **Purpose:** This is the user-facing component. It provides the interactive command-line interface (REPL), handles user input, displays output from Gemini, and manages the overall user experience.
- **Key Features:**
- Input processing (parsing commands, text prompts).
- History management.
- Display rendering (including Markdown, code highlighting, and tool messages).
- [Theme and UI customization](./cli/themes.md).
- Communication with the Core package.
- Manages user configuration settings specific to the CLI.
2. **Core Package (`packages/core`):**
- **Purpose:** This acts as the backend for the CLI. It receives requests from the CLI, orchestrates interactions with the Gemini API, and manages the execution of available tools.
- **Key Features:**
- API client for communicating with the Google Gemini API.
- Prompt construction and management.
- Tool registration and execution logic.
- State management for conversations or sessions.
- Manages server-side configuration.
3. **Tools (`packages/core/src/tools/`):**
- **Purpose:** These are individual modules that extend the capabilities of the Gemini model, allowing it to interact with the local environment (e.g., file system, shell commands, web fetching).
- **Interaction:** The Core package invokes these tools based on requests from the Gemini model. The CLI then displays the results of tool execution.
## Interaction Flow
A typical interaction with the Gemini CLI follows this general flow:
1. **User Input:** The user types a prompt or command into the CLI (`packages/cli`).
2. **Request to Core:** The CLI package sends the user's input to the Core package (`packages/core`).
3. **Core Processes Request:** The Core package:
- Constructs an appropriate prompt for the Gemini API, possibly including conversation history and available tool definitions.
- Sends the prompt to the Gemini API.
4. **Gemini API Response:** The Gemini API processes the prompt and returns a response. This response might be a direct answer or a request to use one of the available tools.
5. **Tool Execution (if applicable):**
- If the Gemini API requests a tool, the Core package prepares to execute it.
- **User Confirmation for Potentially Impactful Tools:** If the requested tool can modify the file system (e.g., file edits, writes) or execute shell commands, the CLI (`packages/cli`) displays a confirmation prompt to the user. This prompt details the tool and its arguments, and the user must approve the execution. Read-only operations (e.g., reading files, listing directories) may not always require this explicit confirmation step.
- If confirmed (or if confirmation is not required for the specific tool), the Core package identifies and executes the relevant tool (e.g., `read_file`, `run_shell_command`).
- The tool performs its action (e.g., reads a file from the disk).
- The result of the tool execution is sent back to the Gemini API by the Core.
- The Gemini API processes the tool result and generates a final response.
6. **Response to CLI:** The Core package sends the final response (or intermediate tool messages) back to the CLI package.
7. **Display to User:** The CLI package formats and displays the response to the user in the terminal.
## Diagram (Conceptual)
```mermaid
graph TD
User[User via Terminal] -- Input --> CLI[packages/cli]
CLI -- Request --> Core[packages/core]
Core -- Prompt/ToolInfo --> GeminiAPI[Gemini API]
GeminiAPI -- Response/ToolCall --> Core
Core -- ToolDetails --> CLI
CLI -- UserConfirms --> Core
Core -- ExecuteTool --> Tools[Tools e.g., read_file, shell]
Tools -- ToolResult --> Core
Core -- FinalResponse --> CLI
CLI -- Output --> User
classDef userStyle fill:#FFFFFF,stroke:#333333,stroke-width:2px
classDef cliStyle fill:#FBBC05,stroke:#000000,stroke-width:2px
classDef coreStyle fill:#34A853,stroke:#000000,stroke-width:2px
classDef apiStyle fill:#4285F4,stroke:#3F51B5,stroke-width:2px
classDef toolsStyle fill:#EA4335,stroke:#000000,stroke-width:2px
class User userStyle
class CLI cliStyle
class Core coreStyle
class GeminiAPI apiStyle
class Tools toolsStyle
```
## Key Design Principles
- **Modularity:** Separating the CLI (frontend) from the Core (backend) allows for independent development and potential future extensions (e.g., different frontends for the same server).
- **Extensibility:** The tool system is designed to be extensible, allowing new capabilities to be added.
- **User Experience:** The CLI focuses on providing a rich and interactive terminal experience.
This overview should provide a foundational understanding of the Gemini CLI's architecture. For more detailed information, refer to the specific documentation for each package and the development guides.