Documentation
Local API Server

Local API Server

Jan includes a built-in API server that is compatible with OpenAI's API specification, allowing you to interact with AI models through a local HTTP interface. This means you can use Jan as a drop-in replacement for OpenAI's API, but running entirely on your computer.

Jan uses Cortex as its core engine for running AI models. If you need a standalone API server without Jan's desktop interface (for example, in server environments or for command-line usage), you can use Cortex directly: https://cortex.so (opens in a new tab).

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Full API documentation is available at Cortex's API Reference (opens in a new tab).


Local API Server


Start Server

Step 1: Start Server

  1. Navigate to the Local API Server
  2. Configure Server Settings
  3. Click Start Server button
  4. Wait for the confirmation message in the logs panel, your server is ready when you see: JAN API listening at: http://127.0.0.1:1337

Step 2: Test Server

The easiest way to test your server is through the API Playground:

  1. Click the API Playground button to open its testing interface
  2. Select a model from the dropdown menu in Jan interface
  3. Try a simple chat completion (opens in a new tab) request
  4. View the response in real-time

Step 3: Use the API

Navigate to Cortex's API Reference (opens in a new tab) to see full API endpoints for your use case.

Server Settings

Host Address Options

  • 127.0.0.1 (Recommended):
    • Only accessible from your computer
    • Most secure option for personal use
  • 0.0.0.0:
    • Makes server accessible from other devices on your network
    • Use with caution and only when necessary

Port Number

  • Default: 1337
  • Can be any number between 1-65535
  • Avoid common ports (80, 443, 3000, 8080) that might be used by other applications

API Prefix

Cross-Origin Resource Sharing (CORS)

CORS controls which websites can access your API, which is important for web applications running in browsers.

When to enable:

  • If you're building a web application that needs to access the API
  • If you're using browser extensions

When to leave disabled:

  • If you're only using the API from your local applications
  • If you're concerned about security

Verbose Server Logs

Enable to show:

  • Detailed information about each API request
  • Error messages and debugging information
  • Server status updates

Troubleshooting Guide

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Enable Verbose Server Logs for detailed error messages.

1. Common Issues

  • Confirm the server is running

  • Check if model is successfully loaded in Jan

  • Check if the port is already in use by another application

  • Verify you have admin/sudo rights if needed

  • Make sure your API endpoint matches your server settings. Example: Using http://localhost:1337 when you set a different port.

  • Make sure the model name in your API request matches exactly what's shown in Jan. Example: If you selected "Llama 3.2 1B Instruct Q8" in Jan, use llama3.2-1b-instruct in your API request.

  • Verify your JSON request format is correct

  • Verify firewall settings

  • Look for detailed error messages in the logs

2. CORS Errors in Web Apps

  • Enable CORS in server settings if using from a webpage
  • Verify the origin of the request
  • Verify your web app's request URL matches the server address exactly
  • Check browser console for specific error messages

3. Performance Issues

  • Monitor system resources (CPU, RAM, and GPU usage)
  • Try to reduce the context length or ngl (number of GPU layers)
  • Check for other resource-intensive applications
Settingsllama.cpp