Shell and execution tools let the agent run commands and code directly on the host system. These tools are not read-only and require explicit permission grants.
| Tool | Description | Read-only |
|---|
BashTool | Execute shell commands in bash | No |
PowerShellTool | Execute PowerShell commands (Windows) | No |
REPLTool | Run code in a persistent REPL session (Python, Node, etc.) | No |
Permission rules
Permission rules for BashTool use the syntax Bash(<pattern>). The pattern is matched against the full command string.
Bash(git *) # Allow all git subcommands
Bash(npm run *) # Allow npm scripts
Bash(cat *) # Allow reading files via cat
Bash(ls *) # Allow directory listings
Bash(git *)
Bash(npm run build)
Bash(npm run test)
Avoid using Bash(*) (allow all) in shared or automated environments. A wildcard rule lets the agent run any command with no prompting, including destructive ones like rm -rf.
BashTool runs each command in a fresh subshell by default. Environment variables and working directory changes do not persist between calls. Use REPLTool if you need a stateful session.
Examples
// Run a test suite
BashTool({ command: 'npm run test' })
// Stage and commit changes
BashTool({ command: 'git add -A && git commit -m "fix: update config"' })
// Check disk usage
BashTool({ command: 'du -sh ./dist' })
BashTool but targets the PowerShell runtime. Permission rules use the same wildcard syntax:
PowerShell(git *)
PowerShell(Get-ChildItem *)
PowerShellTool is only active when Claude Code is running on Windows. On macOS and Linux, BashTool is used instead.
BashTool, a REPL session maintains state across calls — variables, imports, and function definitions persist for the duration of the session.
Supported runtimes include Python and Node.js.
// Define a variable in one call
REPLTool({ language: 'python', code: 'x = [1, 2, 3]' })
// Reference it in the next
REPLTool({ language: 'python', code: 'print(sum(x))' })
// => 6
REPLTool when you need to:
- Run multi-step data transformations that build on previous results
- Test small code snippets interactively during development
- Avoid re-importing libraries or re-loading data on every call
