Prompts

Prompt manipulation is the primary way that you, as an app developer, influence the output of generative AI models. For example, when using LLMs, you can craft prompts that influence the tone, format, length, and other characteristics of the models’ responses.

Genkit is designed around the premise that prompts are code. You write and maintain your prompts in source files, track changes to them using the same version control system that you use for your code, and you deploy them along with the code that calls your generative AI models.

Most developers will find that the included Dotprompt library meets their needs for working with prompts in Genkit. However, alternative approaches are also supported by working with prompts directly.

Defining prompts

Genkit's generate() helper function accepts string prompts, and you can call models this way for straight-forward use cases.

import { generate } from '@genkit-ai/ai';

generate({
  model: 'googleai/gemini-pro',
  prompt: 'You are a helpful AI assistant named Walt.',
});

In most cases, you will need to include some customer provided inputs in your prompt. You could define a function to render them like this.

function helloPrompt(name: string) {
  return `You are a helpful AI assistant named Walt. Say hello to ${name}.`;
}

generate({
  model: 'googleai/gemini-pro',
  prompt: helloPrompt('Fred'),
});

One shortcoming of defining prompts in your code is that testing requires executing them as part of a flow. To faciliate more rapid iteration, Genkit provides a facility to define your prompts and run them in the Developer UI.

Use the definePrompt function to register your prompts with Genkit.

import { definePrompt } from '@genkit-ai/ai';
import z from 'zod';

export const helloPrompt = definePrompt(
  {
    name: 'helloPrompt',
    inputSchema: z.object({ name: z.string() }),
  },
  async (input) => {
    const promptText = `You are a helpful AI assistant named Walt.
    Say hello to ${input.name}.`;

    return {
      messages: [{ role: 'user', content: [{ text: promptText }] }],
      config: { temperature: 0.3 }
    });
  }
);

A prompt action defines a function that returns a GenerateRequest object which can be used with any model. Optionally, you can also define an input schema for the prompt, which is analagous to the input schema for a flow. Prompts can also define any of the common model configuration options, such as temperature or number of output tokens.

You can use this prompt in your code with the renderPrompt() helper function. Provide the input variables expected by the prompt, and the model to call.

import { generate, render } from '@genkit-ai/ai';

generate(
  renderPrompt({
    prompt: helloPrompt,
    input: { name: 'Fred' },
    model: 'googleai/gemini-pro',
  })
);

In the Genkit Developer UI, you can run any prompt you have defined in this way. This allows you to experiment with individual prompts outside of the scope of the flows in which they might be used.

Dotprompt

Genkit includes the Dotprompt library which adds additional functionality to prompts.

  • Loading prompts from .prompt source files
  • Handlebars-based templates
  • Support for multi-turn prompt templates and multimedia content
  • Concise input and output schema definitions
  • Fluent usage with generate()