Inngest Durable Functions

Master Inngest's durable execution model for building fault-tolerant, long-running workflows. This skill covers the complete lifecycle from triggers to error handling.

These skills are focused on TypeScript. For Python or Go, refer to the Inngest documentation for language-specific guidance. Core concepts apply across all languages.

Core Concepts You Need to Know

Durable Execution Model

• Each step should encapsulate side-effects and non-deterministic code
• Memoization prevents re-execution of completed steps
• State persistence survives infrastructure failures
• Automatic retries with configurable retry count

Step Execution Flow

// ❌ BAD: Non-deterministic logic outside steps
async ({ event, step }) => {
  const timestamp = Date.now(); // This runs multiple times!

  const result = await step.run("process-data", () => {
    return processData(event.data);
  });
};

// ✅ GOOD: All non-deterministic logic in steps
async ({ event, step }) => {
  const result = await step.run("process-with-timestamp", () => {
    const timestamp = Date.now(); // Only runs once
    return processData(event.data, timestamp);
  });
};

Function Limits

Every Inngest function has these hard limits:

• Maximum 1,000 steps per function run
• Maximum 4MB returned data for each step
• Maximum 32MB combined function run state including, event data, step output, and function output
• Each step = separate HTTP request (~50-100ms overhead)

If you're hitting these limits, break your function into smaller functions connected via step.invoke() or step.sendEvent().

When to Use Steps

Always wrap in step.run():

• API calls and network requests
• Database reads and writes
• File I/O operations
• Any non-deterministic operation
• Anything you want retried independently on failure

Never wrap in step.run():

• Pure calculations and data transformations
• Simple validation logic
• Deterministic operations with no side effects
• Logging (use outside steps)

Function Creation

Basic Function Structure

const processOrder = inngest.createFunction(
  {
    id: "process-order", // Unique, never change this
    triggers: [{ event: "order/created" }],
    retries: 4, // Default: 4 retries per step
    concurrency: 10 // Max concurrent executions
  },
  async ({ event, step }) => {
    // Your durable workflow
  }
);

Step IDs and Memoization

// Step IDs can be reused - Inngest handles counters automatically
const data = await step.run("fetch-data", () => fetchUserData());
const more = await step.run("fetch-data", () => fetchOrderData()); // Different execution

// Use descriptive IDs for clarity
await step.run("validate-payment", () => validatePayment(event.data.paymentId));
await step.run("charge-customer", () => chargeCustomer(event.data));
await step.run("send-confirmation", () => sendEmail(event.data.email));

Triggers and Events

Event Triggers

Triggers are defined in the triggers array in the first argument of createFunction:

// Single event trigger
inngest.createFunction(
  { id: "my-fn", triggers: [{ event: "user/signup" }] },
  async ({ event }) => { /* ... */ }
);

// Event with conditional filter
inngest.createFunction(
  { id: "my-fn", triggers: [{ event: "user/action", if: 'event.data.action == "purchase" && event.data.amount > 100' }] },
  async ({ event }) => { /* ... */ }
);

// Multiple triggers (up to 10)
inngest.createFunction(
  {
    id: "my-fn",
    triggers: [
      { event: "user/signup" },
      { event: "user/login", if: 'event.data.firstLogin == true' },
      { cron: "0 9 * * *" } // Daily at 9 AM
    ]
  },
  async ({ event }) => { /* ... */ }
);

Cron Triggers

// Basic cron
inngest.createFunction(
  { id: "my-fn", triggers: [{ cron: "0 */6 * * *" }] }, // Every 6 hours
  async ({ step }) => { /* ... */ }
);

// With timezone
inngest.createFunction(
  { id: "my-fn", triggers: [{ cron: "TZ=Europe/Paris 0 12 * * 5" }] }, // Fridays at noon Paris time
  async ({ step }) => { /* ... */ }
);

// Combine with events
inngest.createFunction(
  {
    id: "my-fn",
    triggers: [
      { event: "manual/report.requested" },
      { cron: "0 0 * * 0" } // Weekly on Sunday
    ]
  },
  async ({ event, step }) => { /* ... */ }
);

Function Invocation

// Invoke another function as a step
const result = await step.invoke("generate-report", {
  function: generateReportFunction,
  data: { userId: event.data
how to use inngest-durable-functions
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How to use inngest-durable-functions on Cursor
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1
Prerequisites
Before installing skills in Cursor, ensure your development environment meets these requirements:
›Cursor installed and configured on your development machine
›Node.js version 16.0+ with npm package manager (verify with node --version)
›Active project directory or workspace where you want to add inngest-durable-functions
2
Execute installation command
Execute the skills CLI command in your project's root directory to begin installation:
$npx skills add https://github.com/inngest/inngest-skills --skill inngest-durable-functionscopy
The skills CLI fetches inngest-durable-functions from GitHub repository inngest/inngest-skills and configures it for Cursor.
3
Select Cursor when prompted
The CLI will show a list of available agents. Use arrow keys to navigate and space to select Cursor:
◆ Which agents do you want to install to?
│
│ ── Universal (.agents/skills) ── always included ────
│   • Amp
│   • Antigravity
│   • Cline
│   • Codex
│ ●Cursor(selected)
│   • Cursor
│   • Windsurf
4
Verify installation
Confirm successful installation by checking the skill directory location:
.cursor/skills/inngest-durable-functions
Reload or restart Cursor to activate inngest-durable-functions. Access the skill through slash commands (e.g., /inngest-durable-functions) or your agent's skill management interface.
⚠
Security & Verification Notice
We perform automated surface-level scans (Gen AI Scanner, Socket, Snyk) during installation. These checks detect common vulnerabilities but do not guarantee complete security. Always review skill source code and verify the publisher's reputation before production use.
Skills execute code in your development environment. Always verify the publisher's identity, review recent commits, and test in isolated environments before production deployment.
Additional Resources
›View source code on GitHub›Skills CLI documentation›Learn more about Cursor›What are agent skills?