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Add a custom function (tool) to a phone number so the AI can call your own HTTPS endpoint during a call and use the result. Configured per phone number. Up to 15 functions per number.

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Add a custom function

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string
required
The phone number in E.164 format, passed in the URL.
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string
required
Tool name in snake_case (lowercase letters, numbers, underscores), max 64 characters. Must be unique on the number.
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string
required
Your HTTPS endpoint the AI will call. https only.
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string
Tells the AI when to call this tool. A clear, specific description is how the AI picks the right tool.
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string
default:"POST"
HTTP method: GET, POST, PUT, PATCH, or DELETE.
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object
JSON Schema for the arguments the AI collects. Defaults to an empty object schema.
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object
Optional headers sent with the request (for example an API key). Values support {{variable}} substitution.
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string
What the AI says out loud while the function runs. Prevents silence on slow calls. Optional.
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integer
default:"5000"
How long to wait for your endpoint, in milliseconds. Clamped to 1000-45000 (1-45 seconds).
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boolean
default:"true"
Whether the function is available on calls.
Returns 409 if a function with that name already exists on the number, or a limit_reached error if the number already has 15 functions.

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List custom functions

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Edit a custom function

Update one or more fields of an existing function by its id. Only the fields you send are changed; everything else stays the same.
Editable fields: name, description, url, method, headers, parameters, speak_during, timeout_ms, is_active. Returns 404 if the function id is not found on the number, or 409 if the new name clashes with an existing function on that number.

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Remove a custom function

Delete a specific function by its id:

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Notes

  • The number must belong to your account. A number you do not own returns 404.
  • For how custom functions work in a call, see Custom functions.