Genkit Express Plugin

This plugin provides utilities for conveninetly exposing Genkit flows and actions via Express HTTP server as REST APIs.

See official documentation for more.

Installation

To use this plugin, install it in your project:

npm i @genkit-ai/express

Usage

import { expressHandler } from '@genkit-ai/express';
import express from 'express';

const simpleFlow = ai.defineFlow('simpleFlow', async (input, { sendChunk }) => {
  const { text } = await ai.generate({
    model: googleAI.model('gemini-2.5-flash'),
    prompt: input,
    onChunk: (c) => sendChunk(c.text),
  });
  return text;
});

const app = express();
app.use(express.json());

app.post('/simpleFlow', expressHandler(simpleFlow));

app.listen(8080);

You can also handle auth using context providers:

import { UserFacingError } from 'genkit';
import { ContextProvider, RequestData } from 'genkit/context';

const context: ContextProvider<Context> = (req: RequestData) => {
  if (req.headers['authorization'] !== 'open sesame') {
    throw new UserFacingError('PERMISSION_DENIED', 'not authorized');
  }
  return {
    auth: {
      user: 'Ali Baba',
    },
  };
};

app.post(
  '/simpleFlow',
  authMiddleware,
  expressHandler(simpleFlow, { context })
);

Flows and actions exposed using the expressHandler function can be accessed using genkit/beta/client library:

import { runFlow, streamFlow } from 'genkit/beta/client';

const result = await runFlow({
  url: `http://localhost:${port}/simpleFlow`,
  input: 'say hello',
});

console.log(result); // hello

// set auth headers (when using auth policies)
const result = await runFlow({
  url: `http://localhost:${port}/simpleFlow`,
  headers: {
    Authorization: 'open sesame',
  },
  input: 'say hello',
});

console.log(result); // hello

// and streamed
const result = streamFlow({
  url: `http://localhost:${port}/simpleFlow`,
  input: 'say hello',
});
for await (const chunk of result.stream) {
  console.log(chunk);
}
console.log(await result.output);

You can also use startFlowServer to quickly expose multiple flows and actions:

import { startFlowServer } from '@genkit-ai/express';
import { genkit } from 'genkit';

const ai = genkit({});

export const menuSuggestionFlow = ai.defineFlow(
  {
    name: 'menuSuggestionFlow',
  },
  async (restaurantTheme) => {
    // ...
  }
);

startFlowServer({
  flows: [menuSuggestionFlow],
});

You can also configure the server:

startFlowServer({
  flows: [menuSuggestionFlow],
  port: 4567,
  cors: {
    origin: '*',
  },
});

Contributing

The sources for this package are in the main Genkit repo. Please file issues and pull requests against that repo.

Usage information and reference details can be found in official Genkit documentation.

License

Licensed under the Apache 2.0 License.