Reference · Sessions and engines
Built-in tools
What each of Claude's built-in tools does, grouped the way the Tools screen groups them.
Every tool Claude Code itself can call, before any mode or MCP server adds its own.
| Group | Tool | What it does |
|---|---|---|
| Files and code | Read | Opens a file, a PDF, an image or a notebook. |
| Files and code | Write | Creates a file, or replaces one whole. |
| Files and code | Edit | Changes part of a file in place, notebook cells included. |
| Files and code | Search | Finds files by name and searches their contents. |
| Files and code | Language server | Asks the language server for definitions, references and diagnostics. |
| The shell | Bash | Runs shell commands, and reads the output of ones left in the background. |
| The web | Fetch a page | Reads a URL the session was given or found. |
| The web | Search the web | Runs a web search and reads the results. |
| Delegation | Subagents | Hands work to a subagent that runs on its own and reports back. |
| Delegation | Talking to agents | Lists the agents and sessions it can reach, messages them, and reads or stops their work. |
| Delegation | Workflows | Runs a script that orchestrates many subagents at once. |
| Working with you | Ask you a question | Puts a multiple-choice question in the conversation and waits for an answer. |
| Working with you | Task list | Keeps a checklist of what it is working through. |
| Working with you | Plan mode | Moves the session in and out of planning, where it writes a plan before it changes anything. |
| Everything else | Skills and slash commands | Loads a packaged set of instructions for a task, and runs a slash command. |
| Everything else | Scheduling | Schedules itself to wake up later, on an interval or once. |
| Everything else | Notifications | Sends a push notification, and takes a trigger from a remote one. |
Turning a tool off
The Claude tab of Settings carries the same groups, each tool with its own switch. The switch applies app-wide, to every Claude session this app starts. Turning off Bash removes it from every Claude subprocess spawned afterward. A session already running keeps the tools it started with.
A switched-off tool is left out of the list the model sees, so it is never asked for at all. This is stronger than a deny rule on the Permissions screen, where the tool still appears in the list. The call is refused only when it arrives.
Modes names which mode gives a session which of these tools. The MCP tool catalogue names the tools a server or a mode adds beyond this list.