Use fetch() handler

Last updated Apr 21, 2026 A very common use case is to provide the LLM with the ability to perform API calls via function calling.

In this example the LLM will retrieve the weather forecast for the next 5 days. To do so a getWeather function is defined that is passed to the LLM as tool.

The getWeatherfunction extracts the user's location from the request and calls the external weather API via the Workers' Fetch API and returns the result.

Embedded function calling example with fetch()ts

import { runWithTools } from '@cloudflare/ai-utils';

type Env = {
    AI: Ai;
};

export default {
    async fetch(request, env, ctx) {
        // Define function
        const getWeather = async (args: { numDays: number }) => {
            const { numDays } = args;
      // Location is extracted from request based on
      // https://developers.cloudflare.com/workers/runtime-apis/request/#incomingrequestcfproperties
      const lat = request.cf?.latitude
      const long = request.cf?.longitude

      // Interpolate values for external API call
            const response = await fetch(
                `https://api.open-meteo.com/v1/forecast?latitude=${lat}&longitude=${long}&daily=temperature_2m_max,precipitation_sum&timezone=GMT&forecast_days=${numDays}`
            );
            return response.text();
        };
        // Run AI inference with function calling
        const response = await runWithTools(
            env.AI,
            // Model with function calling support
            '@hf/nousresearch/hermes-2-pro-mistral-7b',
            {
                // Messages
                messages: [
                    {
                        role: 'user',
                        content: 'What the weather like the next 5 days? Respond as text',
                    },
                ],
                // Definition of available tools the AI model can leverage
                tools: [
                    {
                        name: 'getWeather',
                        description: 'Get the weather for the next [numDays] days',
                        parameters: {
                            type: 'object',
                            properties: {
                                numDays: { type: 'numDays', description: 'number of days for the weather forecast' },
                            },
                            required: ['numDays'],
                        },
                        // reference to previously defined function
                        function: getWeather,
                    },
                ],
            }
        );
        return new Response(JSON.stringify(response));
    },
} satisfies ExportedHandler<Env>;

Was this helpful?

YesNo

On this page

Use fetch() handler - 图1Docs

{"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/workers-ai/features/function-calling/embedded/examples/fetch/#page","headline":"Use fetch() handler","description":"Learn how to use the fetch() handler in Cloudflare Workers AI to enable LLMs to perform API calls, like retrieving a 5-day weather forecast using function calling.","url":"https://developers.cloudflare.com/workers-ai/features/function-calling/embedded/examples/fetch/","inLanguage":"en","image":"https://developers.cloudflare.com/workers-ai/features/function-calling/embedded/examples/fetch/og.png?v=840b375b65ba0cf7","dateModified":"2026-04-21","publisher":{"@type":"Organization","name":"Cloudflare","description":"One platform for your apps, agents, and workforce. Build, secure, and scale without managing infrastructure","url":"https://www.cloudflare.com/","sameAs":["https://github.com/cloudflare","https://www.linkedin.com/company/cloudflare","https://x.com/cloudflare"],"logo":{"@type":"ImageObject","url":"https://developers.cloudflare.com/logo.svg"},"address":{"@type":"PostalAddress","streetAddress":"101 Townsend St","addressLocality":"San Francisco","addressRegion":"CA","postalCode":"94107","addressCountry":"US"},"contactPoint":[{"@type":"ContactPoint","contactType":"Customer Support","url":"https://support.cloudflare.com/","availableLanguage":["English"]},{"@type":"ContactPoint","contactType":"Sales","url":"https://www.cloudflare.com/contact/","availableLanguage":["English"]}]},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"},"keywords":["AI"]}

description: Learn how to use Cloudflare Workers AI to interact with KV storage, enabling persistent data handling with embedded function calling in a few lines of code. title: Use KV API image: https://developers.cloudflare.com/workers-ai/features/function-calling/embedded/examples/kv/og.png?v=39ed64a561ba3ea0

Skip to content

Documentation Index
Fetch the complete documentation index at: https://developers.cloudflare.com/workers-ai/llms.txt
Use this file to discover all available pages before exploring further.