Tools

Tools define actions an agent can take – such as reading and writing to a source.

A tool represents an action your agent can take, such as running a SQL statement. You can define Tools as a map in the tools section of your tools.yaml file. Typically, a tool will require a source to act on:

kind: tools
name: search_flights_by_number
type: postgres-sql
source: my-pg-instance
statement: |
  SELECT * FROM flights
  WHERE airline = $1
  AND flight_number = $2
  LIMIT 10
description: |
  Use this tool to get information for a specific flight.
  Takes an airline code and flight number and returns info on the flight.
  Do NOT use this tool with a flight id. Do NOT guess an airline code or flight number.
  An airline code is a code for an airline service consisting of a two-character
  airline designator and followed by a flight number, which is a 1 to 4 digit number.
  For example, if given CY 0123, the airline is "CY", and flight_number is "123".
  Another example for this is DL 1234, the airline is "DL", and flight_number is "1234".
  If the tool returns more than one option choose the date closest to today.
  Example:
  {{
      "airline": "CY",
      "flight_number": "888",
  }}
  Example:
  {{
      "airline": "DL",
      "flight_number": "1234",
  }}
parameters:
  - name: airline
    type: string
    description: Airline unique 2 letter identifier
  - name: flight_number
    type: string
    description: 1 to 4 digit number

Specifying Parameters

Parameters for each Tool will define what inputs the agent will need to provide to invoke them. Parameters should be pass as a list of Parameter objects:

parameters:
  - name: airline
    type: string
    description: Airline unique 2 letter identifier
  - name: flight_number
    type: string
    description: 1 to 4 digit number

Basic Parameters

Basic parameters types include string, integer, float, boolean types. In most cases, the description will be provided to the LLM as context on specifying the parameter.

parameters:
  - name: airline
    type: string
    description: Airline unique 2 letter identifier
fieldtyperequireddescription
namestringtrueName of the parameter.
typestringtrueMust be one of “string”, “integer”, “float”, “boolean” “array”
descriptionstringtrueNatural language description of the parameter to describe it to the agent.
defaultparameter typefalseDefault value of the parameter. If provided, required will be false.
requiredboolfalseIndicate if the parameter is required. Default to true.
allowedValues[]stringfalseInput value will be checked against this field. Regex is also supported.
excludedValues[]stringfalseInput value will be checked against this field. Regex is also supported.
escapestringfalseOnly available for type string. Indicate the escaping delimiters used for the parameter. This field is intended to be used with templateParameters. Must be one of “single-quotes”, “double-quotes”, “backticks”, “square-brackets”.
minValueint or floatfalseOnly available for type integer and float. Indicate the minimum value allowed.
maxValueint or floatfalseOnly available for type integer and float. Indicate the maximum value allowed.

Array Parameters

The array type is a list of items passed in as a single parameter. To use the array type, you must also specify what kind of items are in the list using the items field:

parameters:
  - name: preferred_airlines
    type: array
    description: A list of airline, ordered by preference.
    items:
      name: name
      type: string
      description: Name of the airline.
statement: |
  SELECT * FROM airlines WHERE preferred_airlines = ANY($1);
fieldtyperequireddescription
namestringtrueName of the parameter.
typestringtrueMust be “array”
descriptionstringtrueNatural language description of the parameter to describe it to the agent.
defaultparameter typefalseDefault value of the parameter. If provided, required will be false.
requiredboolfalseIndicate if the parameter is required. Default to true.
allowedValues[]stringfalseInput value will be checked against this field. Regex is also supported.
excludedValues[]stringfalseInput value will be checked against this field. Regex is also supported.
itemsparameter objecttrueSpecify a Parameter object for the type of the values in the array.

Note

Items in array should not have a default or required value. If provided, it will be ignored.

Map Parameters

The map type is a collection of key-value pairs. It can be configured in two ways:

  • Generic Map: By default, it accepts values of any primitive type (string, integer, float, boolean), allowing for mixed data.
  • Typed Map: By setting the valueType field, you can enforce that all values within the map must be of the same specified type.

Generic Map (Mixed Value Types)

This is the default behavior when valueType is omitted. It’s useful for passing a flexible group of settings.

parameters:
  - name: execution_context
    type: map
    description: A flexible set of key-value pairs for the execution environment.

Typed Map

Specify valueType to ensure all values in the map are of the same type. An error will be thrown in case of value type mismatch.

parameters:
  - name: user_scores
    type: map
    description: A map of user IDs to their scores. All scores must be integers.
    valueType: integer # This enforces the value type for all entries.

Authenticated Parameters

Authenticated parameters are automatically populated with user information decoded from ID tokens that are passed in request headers. They do not take input values in request bodies like other parameters. To use authenticated parameters, you must configure the tool to map the required authServices to specific claims within the user’s ID token.

kind: tools
name: search_flights_by_user_id
type: postgres-sql
source: my-pg-instance
statement: |
  SELECT * FROM flights WHERE user_id = $1
parameters:
  - name: user_id
    type: string
    description: Auto-populated from Google login
    authServices:
      # Refer to one of the `authServices` defined
      - name: my-google-auth
        # `sub` is the OIDC claim field for user ID
        field: sub
fieldtyperequireddescription
namestringtrueName of the authServices used to verify the OIDC auth token.
fieldstringtrueClaim field decoded from the OIDC token used to auto-populate this parameter.

Template Parameters

Template parameters types include string, integer, float, boolean types. In most cases, the description will be provided to the LLM as context on specifying the parameter. Template parameters will be inserted into the SQL statement before executing the prepared statement. They will be inserted without quotes, so to insert a string using template parameters, quotes must be explicitly added within the string.

Template parameter arrays can also be used similarly to basic parameters, and array items must be strings. Once inserted into the SQL statement, the outer layer of quotes will be removed. Therefore to insert strings into the SQL statement, a set of quotes must be explicitly added within the string.

Warning

Because template parameters can directly replace identifiers, column names, and table names, they are prone to SQL injections. Basic parameters are preferred for performance and safety reasons.

Tip

To minimize SQL injection risk when using template parameters, always provide the allowedValues field within the parameter to restrict inputs. Alternatively, for string type parameters, you can use the escape field to add delimiters to the identifier. For integer or float type parameters, you can use minValue and maxValue to define the allowable range.

kind: tools
name: select_columns_from_table
type: postgres-sql
source: my-pg-instance
statement: |
  SELECT {{array .columnNames}} FROM {{.tableName}}
description: |
  Use this tool to list all information from a specific table.
  Example:
  {{
      "tableName": "flights",
      "columnNames": ["id", "name"]
  }}
templateParameters:
  - name: tableName
    type: string
    description: Table to select from
  - name: columnNames
    type: array
    description: The columns to select
    items:
      name: column
      type: string
      description: Name of a column to select
      escape: double-quotes # with this, the statement will resolve to `SELECT "id", "name" FROM flights`
fieldtyperequireddescription
namestringtrueName of the template parameter.
typestringtrueMust be one of “string”, “integer”, “float”, “boolean”, “array”
descriptionstringtrueNatural language description of the template parameter to describe it to the agent.
defaultparameter typefalseDefault value of the parameter. If provided, required will be false.
requiredboolfalseIndicate if the parameter is required. Default to true.
allowedValues[]stringfalseInput value will be checked against this field. Regex is also supported.
excludedValues[]stringfalseInput value will be checked against this field. Regex is also supported.
itemsparameter objecttrue (if array)Specify a Parameter object for the type of the values in the array (string only).

Authorized Invocations

You can require an authorization check for any Tool invocation request by specifying an authRequired field. Specify a list of authServices defined in the previous section.

kind: tools
name: search_all_flight
type: postgres-sql
source: my-pg-instance
statement: |
  SELECT * FROM flights
# A list of `authServices` defined previously
authRequired:
  - my-google-auth
  - other-auth-service

Tool Annotations

Tool annotations provide semantic metadata that helps MCP clients understand tool behavior. These hints enable clients to make better decisions about tool usage and provide appropriate user experiences.

Available Annotations

annotationtypedefaultdescription
readOnlyHintboolfalseTool only reads data, no modifications to the environment.
destructiveHintbooltrueTool may create, update, or delete data.
idempotentHintboolfalseRepeated calls with same arguments have no additional effect.
openWorldHintbooltrueTool interacts with external entities beyond its local environment.

Specifying Annotations

Annotations can be specified in YAML tool configuration:

tools:
  my_query_tool:
    kind: mongodb-find-one
    source: my-mongodb
    description: Find a single document
    database: mydb
    collection: users
    annotations:
      readOnlyHint: true
      idempotentHint: true

Default Annotations

If not specified, tools use sensible defaults based on their operation type:

  • Read operations (find, aggregate, list): readOnlyHint: true
  • Write operations (insert, update, delete): destructiveHint: true, readOnlyHint: false

MCP Client Response

Annotations appear in the tools/list MCP response:

{
  "name": "my_query_tool",
  "description": "Find a single document",
  "annotations": {
    "readOnlyHint": true
  }
}

Using tools with MCP Toolbox Client SDKs

Once your tools are defined in your configuration, you can retrieve them directly from your application code.

Here is how to load and invoke your tools across our supported languages:

Python

# Loading a single tool
tool = await toolbox.load_tool("my-tool")

# Invoke the tool
result = await tool("foo", bar="baz")

Javascript/Typescript

// Loading a single tool
const tool = await client.loadTool("my-tool")

// Invoke the tool
const result = await tool({a: 5, b: 2})

Go

// Loading a single tool
tool, err = client.LoadTool("my-tool", ctx)

// Invoke the tool
inputs := map[string]any{"location": "London"}
result, err := tool.Invoke(ctx, inputs)

To see all supported sources and the specific tools they unlock, explore the full list of our Integrations.


Invoke Tools via CLI

Learn how to invoke your tools directly from the command line using the invoke command.