Tools

AI SDK tools run through ML Kit’s function calling. Gemini Nano picks a function and its arguments, the AI SDK runs your tool’s execute in JavaScript, and sends the result back for the next step.

ML Kit’s agent library (genai-agent) only runs tools declared as Android App Functions at build time, so AI SDK tools go through the Prompt API’s function calling instead.

Requirements

Function calling needs Gemini Nano 4. On the Samsung Galaxy Z Flip 8 and Fold 8, the default model is Gemini Nano 4. Elsewhere, ML Kit serves it as the preview release with the fast preference:

• Select the model with releaseStage: 'preview' and preference: 'fast'.
• The device’s Google account must be in the AICore developer preview, and the AICore app must list “Gemini Nano 4 Fast”.

Check features in getModelInfo() for 'functionCalling'. Without it, ML Kit fails any request that declares functions, so the provider sends the request without the tools and returns an unsupported warning for tools. Gemini Nano then answers in text.

Calling Tools

import { createAndroidProvider } from '@react-native-ai/android'
import { generateText, isStepCount, tool } from 'ai'
import { z } from 'zod'

const nano = createAndroidProvider({
  model: { releaseStage: 'preview', preference: 'fast' },
})

const { text } = await generateText({
  model: nano(),
  stopWhen: isStepCount(3),
  tools: {
    getWeather: tool({
      description: 'Gets the current weather in a city.',
      inputSchema: z.object({ city: z.string() }),
      execute: async ({ city }) => ({ city, condition: 'sunny', temperatureC: 24 }),
    }),
  },
  prompt: 'What is the weather in Paris?',
})

Without stopWhen, generateText stops after the tool call, with finishReason: 'tool-calls'.

Tool calls stream as whole tool-call parts, not argument by argument, since ML Kit returns each call complete.

Schemas

Tool input schemas are converted to ML Kit’s FunctionSchema: type (with null for nullable), description, properties, required, enum, format, items, anyOf, title and the length, item, property and number limits. Other keywords, such as $ref and oneOf, are left out.

Tool Choice

toolChoice: 'none' sends no tools. 'auto' is the default. 'required' and a specific tool return an unsupported warning, since Gemini Nano decides itself whether to call a function.

Tool Results

Results go back to Gemini Nano as function responses, which are JSON objects: an object result is sent as is, other values as { result }, and errors and denied approvals as { error }.