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Customize tools

Overview​

Use the MCPToolConfig Custom Resource Definition (CRD) to centrally manage which tools an MCP server exposes, and optionally rename tools or override their descriptions. You reference the configuration from an MCPServer using the toolConfigRef field.

  • toolsFilter: allow-list the tools to expose.
  • toolsOverride: rename tools and/or change their descriptions.
  • Same-namespace only: an MCPServer can reference only MCPToolConfig objects in the same namespace.
  • Precedence: toolConfigRef takes precedence over the deprecated spec.tools field on MCPServer.

Define a basic tool filter​

This example exposes only three tools on a server:

toolconfig-basic.yaml
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPToolConfig
metadata:
  name: basic-tool-filter
  namespace: toolhive-system
spec:
  toolsFilter:
    - read_file
    - write_file
    - list_directory
Empty filter

If toolsFilter is omitted or empty, all tools are allowed.

Rename tools and override descriptions​

You can rename tools to clearly distinguish different deployments or scopes, and refine their descriptions to add usage guidance.

A common pattern is running the same MCP server multiple times for different scopes (for example, separate GitHub orgs, repos, or environments). Renaming tools makes intent obvious and helps prevent mistakes.

toolconfig-with-overrides.yaml
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPToolConfig
metadata:
  name: github-tools-config
  namespace: toolhive-system
spec:
  # Only expose GitHub PR-related tools
  toolsFilter:
    - create_pull_request
    - get_pull_request
    - list_pull_requests
    - merge_pull_request

  # You can override name, description, or both (they are independent)
  toolsOverride:
    # Override only the name
    create_pull_request:
      name: github_create_pr

    # Override only the description (keep the original name)
    get_pull_request:
      description: Retrieve details of a specific GitHub pull request

    # Override both name and description
    list_pull_requests:
      name: github_list_prs
      description: List pull requests in a repository

    merge_pull_request:
      name: github_merge_pr
      description: Merge a GitHub pull request

The key in the toolsOverride map is the original tool name; the name field is the user-visible (overridden) name.

Override fields

You can override name or description independently. Leave one unset to keep the original value from the MCP server. Both fields cannot be empty at the same time.

When to rename?

If you run the same server for different scopes (for example, prod vs. sandbox), use distinct tool names like github_prod_create_pr and github_sandbox_create_pr to make intent clear to clients.

Reference the configuration from an MCP server​

Add toolConfigRef to your MCPServer. toolConfigRef takes precedence over the deprecated spec.tools field on MCPServer.

mcpserver-with-toolconfig.yaml
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPServer
metadata:
  name: github
  namespace: toolhive-system
spec:
  image: ghcr.io/github/github-mcp-server
  transport: stdio
  proxyPort: 8080
  toolConfigRef:
    name: github-tools-config
Filtering and overrides together

When you use toolsFilter and toolsOverride together, filter by the user-visible (overridden) names. Tool calls using overridden names are forwarded to the actual tool.

Example: org-scoped tool names​

Run the GitHub MCP twice, once per organization, and rename tools so intent is clear to clients.

github-org-scoped-tools.yaml
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPToolConfig
metadata:
  name: github-acme-tools
  namespace: toolhive-system
spec:
  toolsFilter:
    - github_acme_create_pr
    - github_acme_get_pr
  toolsOverride:
    create_pull_request:
      name: github_acme_create_pr
    get_pull_request:
      name: github_acme_get_pr
---
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPToolConfig
metadata:
  name: github-foocorp-tools
  namespace: toolhive-system
spec:
  toolsFilter:
    - github_foocorp_create_pr
    - github_foocorp_get_pr
  toolsOverride:
    create_pull_request:
      name: github_foocorp_create_pr
    get_pull_request:
      name: github_foocorp_get_pr
---
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPServer
metadata:
  name: github-acme
  namespace: toolhive-system
spec:
  image: ghcr.io/github/github-mcp-server
  transport: stdio
  proxyPort: 8080
  # (Use credentials that scope access to the acme-org here)
  toolConfigRef:
    name: github-acme-tools
---
apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPServer
metadata:
  name: github-foocorp
  namespace: toolhive-system
spec:
  image: ghcr.io/github/github-mcp-server
  transport: stdio
  proxyPort: 8080
  # (Use credentials that scope access to the foo-corp org here)
  toolConfigRef:
    name: github-foocorp-tools

Inspect status and troubleshoot​

Use kubectl to inspect status and track change propagation:

kubectl -n toolhive-system get mcptoolconfigs
kubectl -n toolhive-system get mcptoolconfig github-tools-config -o yaml
kubectl -n toolhive-system get mcpserver github -o yaml
  • If an MCPToolConfig is still referenced, deletion is blocked by a finalizer. Remove all toolConfigRef references first.
  • If an MCPServer references a missing MCPToolConfig, the server enters Failed and the controller logs include the missing name and namespace.