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318318The `tools` option and the allowed/disallowed lists affect two layers: availability, which controls whether a tool appears in Claude's context, and permission, which controls whether a call is approved once Claude attempts it. `tools` and bare-name `disallowedTools` entries change availability. `allowedTools` and scoped `disallowedTools` rules change permission. If you name one of the [task-tracking tools](/docs/en/agent-sdk/todo-tracking#model-availability) in `allowedTools`, Claude Code also opts the session in.
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320| Option | Layer | Effect |
321| :------------------------ | :----------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
322| `tools: ["Read", "Grep"]` | Availability | Only the listed built-ins are in Claude's context. Unlisted built-ins are removed. MCP tools are unaffected. |
323| `tools: []` | Availability | All built-ins are removed. Claude can only use your MCP tools. |
324| allowed tools | Permission | Listed tools run without a permission prompt. Other unlisted tools remain available; calls go through the [permission flow](/docs/en/agent-sdk/permissions). |
325| disallowed tools | Both | A bare tool name such as `"Bash"` removes the tool from Claude's context, the same as omitting it from `tools`. A scoped rule such as `"Bash(rm *)"` leaves the tool in context and denies only matching calls. |
320| Option | Layer | Effect |
321| :------------------------ | :----------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
322| `tools: ["Read", "Grep"]` | Availability | Only the listed built-ins are in Claude's context. Unlisted built-ins are removed. MCP tools are unaffected. |
323| `tools: []` | Availability | All built-ins are removed. Claude can only use your MCP tools. |
324| allowed tools | Permission | Listed tools run without a permission prompt. Other unlisted tools remain available; calls go through the [permission flow](/docs/en/agent-sdk/permissions). |
325| disallowed tools | Both | A bare tool name such as `"Bash"` removes the tool from Claude's context, the same as omitting it from `tools`. A scoped rule such as `"Bash(rm *)"` leaves the tool in context and denies only calls that match [as written](/docs/en/permissions#bash-rule-limits). |
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327327To remove a built-in entirely, omit it from `tools` or list its bare name in `disallowedTools` (Python: `disallowed_tools`); both keep the tool out of context so Claude never attempts it. A scoped `disallowedTools` rule blocks matching calls but leaves the tool visible, so Claude may waste a turn trying it. See [Configure permissions](/docs/en/agent-sdk/permissions) for the full evaluation order.
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