Tool configuration

Customize which languages, parameters, and descriptions the agent sees through your configuration file. These settings change presentation, not sandbox permissions. For interpreter selection and database startup, see Languages and startup. For startup packages and preparation policies, see Package settings. For a guide with examples, see Build a data assistant.

Model-visible languages

Setting	Accepted values	Default
`languages`	Nonempty list of `r`, `python`, and/or `sql`; or `null`	Omitted or `null`: `[r, python, sql]`.

languages: [sql, python]

Choose a nonempty subset of r, python, and sql. A later list replaces the whole list. This controls the tool schema and accepted source fields, not interpreter availability or permissions. SQL can use a hidden R or Python provider. Requirements, polling, input, and controls remain available unless hidden through tool.parameters.

A hidden source field is rejected even when its value is null. Exposing a language does not install its runtime. This is a presentation setting, not a security boundary.

Tool descriptions and parameters

The tool mapping accepts these settings:

Setting	Accepted values	Default and behavior
`tool.description`	String or `null`	Omitted or `null`: generated `send` description. A string replaces it completely.
`tool.instructions`	String or `null`	Omitted or `null`: generated initialization instructions. A string replaces them completely.
`tool.parameters`	Mapping of parameter names to settings	Omission keeps the normal schema and descriptions.

For example:

languages: [python]
tool:
  description: |-
    Run Python code in a persistent session.
    Poll with an empty call when work is still running.
  instructions: Persistent Python session.
  parameters:
    python:
      description: Execute one complete Python cell.
    requirements:
      description: Prepare dependencies before execution.
      parameters:
        python:
          description: Python registry package requirements.
    timeout_ms:
      enabled: false

tool.description replaces the complete send description returned by tools/list. tool.instructions replaces the server instructions returned in the earlier initialize response. Despite their location under tool, instructions describe the server as a whole.

Setting	Lifecycle and purpose
`tool.instructions`	Available to the client when the connection initializes. Introduce the workbench and when to select it; a client may use this text for a server summary or deferred tool search.
`tool.description`	Returned when the client lists tools, alongside `send`’s input schema. Explain when and how to call `send`, including polling, state, and result handling.
`tool.parameters.<name>.description`	Part of that input schema. Explain the corresponding argument and how to supply its value.

The client controls when these texts enter the model’s context. A client can fetch tools/list at connection time while deferring the full definition until the model searches for it. In that workflow, initialization instructions may supply the initial server summary; other clients use their own server description or expose tools immediately. Do not assume instructions are always shown, shown in full, or the only text visible before loading a tool. See deferred tool discovery for client-specific guidance and the protocol references.

Parameter settings

Each entry under tool.parameters.<name> accepts:

Node	Accepted values	Meaning and default
`tool.parameters.<name>.enabled`	`true` or `false`	Advertise and accept the parameter when true. Default: `true`. False hides it and rejects explicitly supplied values, including `null`; omission retains the runtime default.
`tool.parameters.<name>.description`	String or `null`	Replace that parameter’s description. Omitted or `null`: generated text.
`tool.parameters.<name>.parameters`	Mapping of nested parameter names to the same settings	Customize fields inside an object parameter. Omission keeps their defaults; scalar fields accept no nested names.
`tool.parameters.<name>.schema`	Unchanged metadata mapping from `config resolve --full`, or `null`	Read-only inspection of argument types/constraints. Changing metadata is invalid; omit it when writing configuration by hand.

Available top-level names are r, python, sql, requirements, control, stdin, and timeout_ms. Source fields are available only for the selected languages. Under tool.parameters.requirements.parameters, the names are action, r, python, python_version, duckdb, and exclude_newer. Each uses the same parameter settings above.

Each parameter’s description replaces its complete description; nested parameters use another parameters mapping. Strings are used verbatim, including empty strings, without appending generated guidance or permission text. Omitted descriptions and instructions keep their generated text. Override each description you want to change; replacing the tool description does not clear parameter descriptions.

Set enabled: false to remove a parameter from the advertised schema and reject calls that supply it, including null values. Omission keeps the parameter’s existing runtime default. For example, hiding timeout_ms makes every call use the existing 60,000 ms wait budget; work continues after that budget expires, and an empty call polls for more output. Generated timeout guidance follows this choice. Generated Python guidance uses installed packages when requirements.python or its parent requirements field is hidden under explicit resolution. When hiding other parameters, supply matching description overrides if their generated prose refers to the hidden fields.

Parameter settings apply after languages; unknown or unavailable names and nested parameters under scalar fields fail launch. Both serve and ordinary sandbox launches validate these settings before starting a worker or target process. These settings customize descriptions and visibility, while parameter names, types, constraints, and runtime defaults retain their existing contracts. They use the ordinary configuration merge rules and are captured once per server connection. To hide only the timeout through the command line:

mcp-console serve -c tool.parameters.timeout_ms.enabled=false

To inspect generated descriptions and parameter metadata before editing, see Inspect and edit resolved configuration.