How Claude Code uses prompt caching changedprompt-caching
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109109### Denying an entire tool
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111Adding a bare tool name like `Bash` or `WebFetch` as a [deny rule](/docs/en/permissions#manage-permissions) removes that tool from Claude's context entirely. Built-in tool definitions load into the system prompt layer, so adding or removing one of these rules mid-session invalidates the cache. The change takes effect on the next turn whether you add it through `/permissions` or by [editing a settings file directly](/docs/en/settings#when-edits-take-effect).
111Adding a bare tool name like `Bash` or `WebFetch` as a [deny rule](/docs/en/permissions#manage-permissions) removes that tool from Claude's context entirely. Built-in tool definitions load into the system prompt layer, so adding or removing one of these rules mid-session invalidates the cache. Claude Code applies the change on the next request, even one in the middle of a turn, whether you add the rule through `/permissions` or by [editing a settings file directly](/docs/en/settings#when-edits-take-effect).
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113113Only a deny rule that matches in the tool-name position has this effect: a bare tool name, the equivalent `Bash(*)` form, or a [tool-name glob](/docs/en/permissions#tool-name-wildcards) like `"*"`. A glob that matches only MCP tools, such as `"mcp__*"`, removes those tools the same way but leaves the cache intact when the matched tools are [deferred](#connecting-or-disconnecting-an-mcp-server), the default, since deferred definitions were never in the cached prefix. Scoped deny rules like `Bash(rm *)`, and all allow and ask rules, don't change which tools Claude sees. Claude Code checks them when Claude attempts a call, leaving the prefix intact.
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