Tools are the bridge between the LLM's intentions and your local environment. Each tool defines what it can do, what inputs it accepts, and whether it's safe to run in parallel.
The LLM decides which tool to call and with what arguments
The agent validates the input against the tool's schema
Permission checks run (allow/deny/ask based on your rules)
The tool executes and returns a result
The result is sent back to the LLM for the next step
Tool What it does
FileRead Read files with line numbers. Handles text, PDF (via pdftotext), Jupyter notebooks, and images (base64 for vision). FileWrite Create or overwrite files. Auto-creates parent directories. FileEdit Search-and-replace within files. Requires unique match unless replace_all is set. NotebookEdit Edit Jupyter notebook cells (replace, insert, delete).
Tool What it does
Grep Regex content search powered by ripgrep. Supports context lines, glob filtering, case sensitivity. Glob Find files by pattern, sorted by modification time. ToolSearch Discover available tools by keyword or direct name.
Tool What it does
Bash Run shell commands with timeout, background execution, destructive command detection, and output truncation. REPL Execute Python or Node.js code snippets in an interpreter.
Tool What it does
Agent Spawn subagents for parallel tasks with optional git worktree isolation. SendMessage Send messages between running agents. Skill Invoke user-defined skills programmatically.
Tool What it does
EnterPlanMode / ExitPlanMode Toggle read-only mode for safe exploration. TaskCreate / TaskUpdate / TaskGet / TaskList / TaskStop / TaskOutput Full task lifecycle management. TodoWrite Structured todo list management.
Tool What it does
WebFetch HTTP GET with HTML-to-text conversion. WebSearch Web search with result extraction. LSP Language server diagnostics with linter fallbacks.
Tool What it does
McpProxy Calls tools on connected MCP servers. ListMcpResources Browse MCP server resources. ReadMcpResource Read a specific MCP resource by URI.
Tool What it does
EnterWorktree / ExitWorktree Create and manage isolated git worktrees. AskUserQuestion Prompt the user with structured multi-choice questions. Sleep Async pause with cancellation.
Tools declare whether they're safe to run in parallel:
Read-only tools (FileRead, Grep, Glob, etc.) run concurrentlyMutation tools (Bash, FileWrite, FileEdit) run serially
This maximizes throughput while preventing race conditions on file writes.
Tool results larger than 64KB are automatically persisted to disk (~/.cache/agent-code/tool-results/). The conversation receives a truncated preview with a file path reference so the full output isn't lost.
See Custom Tools for how to implement the Tool trait and register new tools.