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Version: 1.1.x

Tool Customization

Tool Customization lets you create modified versions of existing tools with fixed input values, rewritten descriptions, or both. These customized tools appear alongside the originals and can be used to enforce constraints when tools are called by AI agents.

Common use cases:

  • Force tools to run with specific parameters (e.g. always use a fixed timezone)
  • Add or rewrite tool descriptions
  • Expose only the safe variants to agents using ACLs
Example Configuration
toolExtensions:
  services:
    time:
      get_current_time:
        childTools:
          - name: get_current_time_paris
            description:
              action: rewrite
              text: "Get current time in Paris, France."
            overrideParams:
              timezone: Europe/Paris

This creates a new tool called get_current_time_paris that always uses the Europe/Paris timezone, regardless of what the user or agent provides.

create paris time

Description Customization​

You can either:

  • Rewrite the description completely:
description:
  action: rewrite
  text: "Get current time in Paris, France"
  • Or append extra info to the end:
description:
  action: append
  text: "Only works for Paris."

Parameter Overrides​

Use overrideParams to lock specific inputs:

overrideParams:
  timezone: Europe/Paris

When set:

  • That stated value is always used, even if others are provided.
  • The parameter’s description is automatically annotated to clarify that it's fixed.
note
  • Tool Customization is configured in app.yaml or via the MCPX Control Plane.
  • Original servers must already exist (in mcp.json or added through the Control Plane).
  • Customized tools appear in the UI with a special label.