External API limitations

Limits that apply to External API everywhere — supported models, Python runtime, libraries, input schema, and per-character caps.

These limits apply whether you configure External API in the Playground or through the API.

Supported models

External API only runs when the character's model can call tools. That depends on the path you use:

Path	Supported models
Live API (WebRTC)	OpenAI, Claude, and Gemini. Popular open-source models that support tools — including Grok and the DeepSeek family — work here too. Others may work if they support tool calling; check models.dev.
gRPC	OpenAI, Claude, and Gemini family models only.

If the model doesn't support tools, the character still chats normally — it just won't call your External API functions.

Runtime

Rule	Detail
Language	Python only ("language": "python")
Runtime	Python 3.11
Standard library	Allowed (json, datetime, math, re, urllib, and the rest of the stdlib)
Third-party packages	requests only for now
Source code size	At most 400 lines
Entry point	Must define def handle_event(inputs): (single argument; name is fixed)
Return value	JSON-serializable, usually a dict
State	No shared mutable state across calls — each run is independent

Anything outside the standard library and requests fails at runtime.

Input description

input_description is a JSON string (not a nested object in the API body). After parsing, it must look like:

{
  "parameters": {
    "city": {
      "type": "string",
      "description": "Name of the city to look up"
    }
  },
  "required": ["city"]
}

Rule	Detail
Top-level keys	parameters and required are both required
Parameter names	^[a-zA-Z_][a-zA-Z0-9_]*$
Parameter fields	Each parameter needs type and description
Allowed types	string, integer, boolean, object, array
Extra keys under parameters	Not allowed

Keep descriptions concrete. The model fills arguments from that text, so vague wording produces bad calls.

Character limits

Rule	Detail
Active functions per character	At most 128
Unlink vs delete	"status": "inactive" only disconnects a character; delete removes the function from the account and every link

Related

• External API (Playground) — UI setup and examples
• External API (API reference) — create, list, link, unlink, delete