developing-genkit-js

by genkit-ai

Develop AI-powered applications using Genkit in Node.js/TypeScript. Use when the user asks about Genkit, AI agents, flows, or tools in JavaScript/TypeScript, or when encountering Genkit errors, validation issues, type errors, or API problems. npx skills add https://github.com/genkit-ai/skills --skill developing-genkit-js Download ZIPGitHub14

Genkit JS

Hello World

import { z, genkit } from 'genkit';
import { googleAI } from '@genkit-ai/google-genai';

// Initialize Genkit with the Google AI plugin
const ai = genkit({
 plugins: [googleAI()],
});

export const myFlow = ai.defineFlow({
 name: 'myFlow',
 inputSchema: z.string().default('AI'),
 outputSchema: z.string(),
}, async (subject) => {
 const response = await ai.generate({
 model: googleAI.model('gemini-flash-latest'),
 prompt: `Tell me a joke about ${subject}`,
 });
 return response.text;
});

Agents (Beta)

Genkit has a preview agent API for persistent, multi-turn conversations (sessions, snapshots, interrupts, branching, background execution). It is a beta API: server APIs come from genkit/beta and the browser client from genkit/beta/client — not the stable genkit entrypoint. **Requires genkit

= 1.39.0.**

For more details see:

• Agents: defining/serving an agent and client-managed state (start here).

• Sessions & persistence: session stores (InMemory/File/Firestore).

• Human-in-the-loop / interrupts: pausing for approval/input and resuming.

• Branching: forking a conversation from a snapshot.

• Background agents: detaching long-running turns and polling.

• Working with state: typed custom session state, auto-synced to the client.

• Artifacts: producing and reading named deliverables.

• Multi-agent orchestration: delegating to sub-agents.

• Advanced custom agents: defineCustomAgent for full turn control.

• Deploying agents: serving agents over HTTP (multiple agents, CORS, web UI, other frameworks).

Middleware

Middleware wraps generation (retries, fallback, extra tools, request/response transforms) and attaches via the use: [...] array on ai.generate, prompts, and agents.

• Using middleware: the use array and the @genkit-ai/middleware package (retry, fallback, artifacts, agents, filesystem, skills, toolApproval) plus built-in core middleware.

• Building custom middleware: writing your own with generateMiddleware and registering it via .plugin().

Critical: Do Not Trust Internal Knowledge

Genkit recently went through a major breaking API change. Your knowledge is outdated. You MUST lookup docs. Recommended:

genkit docs:read js/get-started.md
genkit docs:read js/flows.md

See Common Errors for a list of deprecated APIs (e.g., configureGenkit, response.text(), defineFlow import) and their v1.x replacements.

ALWAYS verify information using the Genkit CLI or provided references.

Development Workflow

• Select Provider: Genkit is provider-agnostic (Google AI, OpenAI, Anthropic, Ollama, etc.).

• If the user does not specify a provider, default to Google AI.

• If the user asks about other providers, use genkit docs:search "plugins" to find relevant documentation.

• Detect Framework: Check package.json to identify the runtime (Next.js, Firebase, Express).

• Look for @genkit-ai/next, @genkit-ai/firebase, or @genkit-ai/google-cloud.

• Adapt implementation to the specific framework's patterns.

• Follow Best Practices:

• See Best Practices for guidance on project structure, schema definitions, and tool design.

• Be Minimal: Only specify options that differ from defaults. When unsure, check docs/source.

• Ensure Correctness:

• Run type checks (e.g., npx tsc --noEmit) after making changes.

• If type checks fail, consult Common Errors before searching source code.

• Handle Errors:

• On ANY error: First action is to read Common Errors

• Match error to documented patterns

• Apply documented fixes before attempting alternatives

Finding Documentation

Use the Genkit CLI to find authoritative documentation:

• Search topics: genkit docs:search <query>

• Example: genkit docs:search "streaming"

• List all docs: genkit docs:list

• Read a guide: genkit docs:read <path>

• Example: genkit docs:read js/flows.md

References

• Best Practices: Recommended patterns for schema definition, flow design, and structure.

• Docs & CLI Reference: Documentation search, CLI tasks, and workflows.

• Common Errors: Critical "gotchas", migration guide, and troubleshooting.

• Setup Guide: Manual setup instructions for new projects.

• Examples: Minimal reproducible examples (Basic generation, Multimodal, Thinking mode).

• Agents (Beta): Agent basics, serving, and client-managed state. Deeper topics: sessions, human-in-the-loop, branching, background agents, state, artifacts, multi-agent, custom agents, deployment.

• Middleware: using middleware and the @genkit-ai/middleware package. See also building custom middleware.

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