BuildTools

Tool input overrides

Pin a tool's input fields to fixed values.

Tool Description Overrides change what the model reads. Tool input overrides change what the model can send. Where description overrides shape selection (which tool to call), input overrides pin specific arguments (what value a field carries when the call runs).

An input override hardcodes one or more fields on a tool. When a tool call runs, Agent Handler overwrites those fields with your values before the call reaches the third party. Whatever the model produced for an overridden field is replaced. This is how you guarantee every call lands on the same workspace, project, or view without trusting the model to fill the field correctly.

What an override does

For each field you configure, you give a value. At execution time that value replaces whatever the model sent for the field. String inputs are coerced to the field’s type, so "25" becomes 25 when the schema expects an integer. Fields you don’t configure pass through untouched.

Overrides are keyed by field path, with dot notation for nested fields. The stored shape for a tool that takes an input_data object looks like this:

1{
2  "input_data.view": "cases",
3  "input_data.fields": ["id", "status"],
4  "sort.field": "created_at"
5}

A configured field is always replaced. There is no “fill only when the model omits it” behavior, so treat an override as a hard pin rather than a default.

When to use them

Pin a fixed value

You’re building an agent for one Slack workspace, and you don’t want the model to ever choose which workspace a message goes to. Pin workspace_id on slack__post_message to your workspace ID. Every call uses that value, even if the model tries to set a different one.

Hold a field constant across an integration

If every call should write to the same project, board, or view, pin that field once on the tool instead of depending on the system prompt to repeat it on every turn.

Scope

An override is set per connector and tool, and it applies organization-wide. There is at most one override per connector and tool combination. Overrides are not scoped per Tool Pack: an overridden connector tool behaves the same way across every Tool Pack in the organization.

Configure in the dashboard

Open the connector in the dashboard, then the tool, and set values for the fields you want to pin.

What input overrides don’t do

  • They don’t hide the field from the model. The model still sees the field in the tool schema, and its value is replaced at execution time.
  • They don’t narrow enums or rename fields. A configured field is replaced with one fixed value, nothing more.
  • They don’t relax the tool’s schema. If your pinned value violates the tool’s input schema, the connector rejects the call before it reaches the third party.
  • They aren’t a substitute for a purpose-built tool. If you find yourself pinning many fields to reshape a tool, a custom MCP server with a tool built for the job is the better fit. See Custom MCP servers.

Next

Connect your agent to Agent Handler over MCP in MCP integration.