> ## Documentation Index > Fetch the complete documentation index at: https://docs.limitless.exchange/llms.txt > Use this file to discover all available pages before exploring further. # Market Maker Heartbeat > A safety timer for your orders. Set a deadline, then keep extending it while your trading service runs. If updates stop and the deadline passes, Limitless starts canceling your open orders across all markets. This does not block new orders, so stop placing them if an update fails. ## Set or update a deadline Send `cancelAt` as a Unix timestamp in **milliseconds**. It must be a whole number at least five seconds later than server time. Each successful request replaces your previous deadline. The timestamp below is an example; calculate a new one for each request. ```json theme={null} { "cancelAt": 1800000010000 } ``` Update the deadline early enough to allow for network delays and clock differences. If an update fails, **stop placing new orders** until an update succeeds. The API does not block new orders when the deadline passes. ## Turn off the timer Send an empty JSON object to remove your deadline: ```json theme={null} {} ``` This also succeeds if no deadline is set. Once the deadline passes and cancellation starts, updating or removing the deadline cannot stop it. ## Authentication and results Authenticate as the profile whose orders you want to cover. If you use a scoped API token, it needs the `trading` scope. Sign the exact JSON body and `/heartbeats` path; see [HMAC request signing](/developers/authentication#hmac-request-signing). This endpoint does not accept `onBehalfOf`: a partner token cannot set a deadline for a sub-account. * `200 OK`: deadline set, updated, or removed. No response data is returned. * `400 Bad Request`: `cancelAt` is invalid or too close to server time. * `401 Unauthorized`: authentication or profile is missing. * `403 Forbidden`: the API token lacks the `trading` scope. * `409 Conflict` with `errorCode: "cancellation_in_progress"`: the deadline passed and cancellation has started. Stop placing orders. You can set a new deadline after cancellation finishes. Cancellation may take time, and some orders may remain open, especially orders submitted after the deadline. Do not assume every order was canceled. [Check your orders](/api-reference/trading/user-orders) in each market to see which are still open. ## OpenAPI ````yaml POST /heartbeats openapi: 3.0.0 info: title: Limitless Exchange API description: >- # Limitless Exchange Trading API *Production-ready API for prediction market trading, portfolio management, and market data* > 🎯 **Quick Navigation**: [Authentication](#tag/authentication) | [Markets](#tag/markets) | [Trading](#tag/trading) | [Portfolio](#tag/portfolio) --- ## 🚀 Quick Start Choose your preferred programming language for complete end-to-end implementation: ### Overview The Limitless Exchange API offers both REST and WebSocket integration: **REST API (Trading)**: 1. **🔐 Authentication**: Use API key for all programmatic access 2. **📊 Fetch Market Data**: Get market info including venue contract addresses (once per market) 3. **📋 Order Creation**: Build and sign orders using EIP-712 structured data 4. **🚀 Order Submission**: Submit signed orders and receive confirmations **WebSocket API (Real-Time Data)**: 1. **🔌 Connection**: Connect to `/markets` namespace for real-time updates 2. **📊 Subscriptions**: Subscribe to market prices and position changes 3. **📡 Events**: Handle live market data and transaction updates ### 🔐 Authentication for API Users > **⚠️ DEPRECATION NOTICE**: Cookie-based session authentication is deprecated and will be removed within weeks. Please migrate to API keys immediately. | Method | Header | Status | |--------|--------|--------| | **API Key** | `X-API-Key: lmts_...` | ✅ Required for programmatic access | | Cookie Session | `Cookie: limitless_session=...` | ⚠️ Deprecated (removal imminent) | **Getting an API Key** API keys can only be created via the Limitless Exchange UI: 1. Log in to [limitless.exchange](https://limitless.exchange) using your wallet 2. Click your profile menu (top right) 3. Select "Api keys" 4. Generate a new key **Using Your API Key** Include in all requests via the `X-API-Key` header: ```bash # REST API curl -H "X-API-Key: lmts_your_key_here" https://api.limitless.exchange/markets # WebSocket - pass X-API-Key header during connection handshake ``` ### Migration from Cookie to API Key If you're currently using cookie-based authentication, migrate by: 1. **Generate an API key** via the UI (profile menu → Api keys) 2. **Replace cookie header** with API key header: ```diff # Before (deprecated) - Cookie: limitless_session=your_session_token # After + X-API-Key: lmts_your_key_here ``` 3. **Remove session management code** - no more login flow or cookie handling needed ### Important: Venue System for CLOB Markets CLOB markets use a **venue system** where each market is associated with specific contract addresses. Before placing orders: 1. **Fetch market data once**: `GET /markets/:slug` returns venue information 2. **Use venue.exchange**: This is the `verifyingContract` for EIP-712 order signing 3. **Cache the venue**: Venue data is static per market - fetch once and reuse **Sample venue response:** ```json { "venue": { "exchange": "0xA1b2C3...", "adapter": "0xD4e5F6..." } } ``` ### Required Approvals Before trading, set up token approvals based on order type: | Order Type | Market Type | Approve To | |------------|-------------|------------| | BUY | All CLOB | USDC → `venue.exchange` | | SELL | Simple CLOB | CT → `venue.exchange` | | SELL | NegRisk/Grouped | CT → `venue.exchange` AND `venue.adapter` | ### Checksummed Addresses All addresses must use **checksummed format** (EIP-55 mixed-case): - Authentication: `x-account` header - Orders: `maker` and `signer` fields - Example: `0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed` ### Implementation Guides **[🐍 Python Quick Start](#description/-python-quick-start)** - REST API: eth-account, requests, and web3.py libraries - WebSocket: python-socketio, asyncio integration **[☕ Java Quick Start](#description/-java-quick-start)** - REST API: Web3j, OkHttp3, and Jackson libraries **[📦 Node.js/TypeScript Quick Start](#description/-nodejs-typescript-quick-start)** - REST API: viem, ethers, and cross-fetch libraries - WebSocket: socket.io-client for real-time trading - Full TypeScript support with end-to-end examples **[🔌 WebSocket Integration](#description/-websocket-integration)** - Real-time market data and position updates - Production-ready Python client with authentication --- ## 🐍 Python Quick Start Complete end-to-end Python implementation for Limitless Exchange API integration. ### 🐍 Python E2E Order Creation Guide Complete Python implementation guide is being loaded from external documentation... **Guide Contents:** - 🔐 Complete authentication flow with eth-account - 📋 Order construction with Web3.py calculations - ✍️ EIP-712 structured data signing - 🚀 Order submission with requests library - ⚠️ Comprehensive error handling - 🛠️ Production deployment considerations *For the complete Python guide, ensure the file is available at docs/scripts-samples/python-e2e-order-creation.md* ## ☕ Java Quick Start Complete end-to-end Java implementation for Limitless Exchange API integration. ### ☕ Java E2E Order Creation Guide Complete Java enterprise implementation guide is being loaded from external documentation... **Guide Contents:** - 🔐 Complete authentication flow with Web3j - 📋 Order construction with BigInteger precision - ✍️ EIP-712 structured data signing - 🚀 Order submission with OkHttp3 - ⚠️ Enterprise error handling patterns - 🏗️ Production Maven project structure *For the complete Java guide, ensure the file is available at docs/scripts-samples/java-e2e-order-creation.md* ## 📦 Node.js/TypeScript Quick Start Complete end-to-end Node.js/TypeScript implementation for trading and WebSocket subscriptions. ### 📦 Node.js/TypeScript Trading & WebSocket Guide Complete Node.js/TypeScript implementation guide is being loaded from external documentation... **Guide Contents:** - 🔐 **Authentication**: Wallet-based auth with ethers and viem - 📋 **Order Creation**: EIP-712 signing with viem WalletClient - 🚀 **Order Submission**: REST API integration with cross-fetch - 🔌 **WebSocket Subscriptions**: socket.io-client for real-time updates - 📊 **Market Data**: AMM prices and CLOB orderbook subscriptions - ⚠️ **Type Safety**: Full TypeScript support with proper types - 🛠️ **Production Ready**: Complete end-to-end working example **Key Features:** - **Combined Subscriptions**: Subscribe to both AMM and CLOB markets simultaneously - **Authentication Flow**: Complete wallet-based authentication with session management - **Trading Integration**: Place orders and receive real-time updates - **TypeScript First**: Type-safe implementation with proper interfaces *For the complete Node.js guide, ensure the file is available at docs/scripts-samples/node-socket-trading-and-subscribe.md* ## 🔌 WebSocket Integration Real-time market data and position updates using WebSocket connections. ### 🔌 WebSocket Real-Time Integration Guide Complete WebSocket implementation guide is being loaded from external documentation... **Guide Contents:** - 🔌 **WebSocket Connection**: python-socketio client with async support - 🔐 **Authentication**: JWT session cookie integration - 📊 **Market Subscriptions**: Real-time price updates and position changes - ⚡ **Event Handling**: Comprehensive event processing patterns - 🔄 **Auto-Reconnection**: Production-ready reconnection logic - 🛠️ **Error Recovery**: Robust error handling and fallback strategies **Key Features:** - **Public Mode**: Market price updates without authentication - **Authenticated Mode**: Full access to positions and transactions - **Multi-Market Support**: Subscribe to multiple markets simultaneously - **Production Ready**: Tested patterns for production deployment *For the complete WebSocket guide, ensure the file is available at docs/scripts-samples/python-socket-subscribe.md* version: '1.0' contact: name: API Support url: https://limitless.exchange email: hey@limitless.network servers: - url: https://api.limitless.exchange description: Production API security: [] tags: - name: Authentication description: User authentication and session management - name: Markets description: Browse, search, and analyze prediction markets - name: Market Navigation description: Navigation tree, market pages, and property filters - name: Trading description: Create, manage, and cancel orders - name: Portfolio description: Position tracking, trade history, and performance - name: Feed description: Public trading activity feeds paths: /heartbeats: post: tags: - Trading summary: Set, update, or turn off an order cancellation deadline description: >- A safety timer for your orders. Set a deadline, then keep extending it while your trading service runs. If updates stop and the deadline passes, Limitless starts canceling your open orders across all markets. This does not block new orders, so stop placing them if an update fails. operationId: HeartbeatController_update requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/UpdateHeartbeatDto' examples: setDeadline: summary: Set or update the deadline (Unix milliseconds) value: cancelAt: 1800000010000 turnOff: summary: Turn off the timer value: {} responses: '200': description: Deadline set, updated, or removed; no response data '400': description: cancelAt must be an integer at least five seconds after server time '401': description: Authentication required or authenticated profile not found '403': description: API token lacks the trading scope '409': description: >- The deadline passed and cancellation started; updating or removing it cannot stop cancellation content: application/json: schema: type: object properties: errorCode: type: string enum: - cancellation_in_progress message: type: string required: - errorCode - message example: errorCode: cancellation_in_progress message: Cancellation in progress security: - HmacAuth: [] components: schemas: UpdateHeartbeatDto: type: object description: >- Include cancelAt to set or update a deadline; send {} to turn off the timer. properties: cancelAt: type: integer description: >- Future Unix timestamp in milliseconds, at least five seconds after server time. Leave out to turn off the timer. example: 1800000010000 securitySchemes: HmacAuth: type: apiKey in: header name: lmts-api-key description: >- Scoped API token with HMAC-SHA256 signing. Requires three headers: lmts-api-key (token ID), lmts-timestamp (ISO-8601), lmts-signature (Base64-encoded HMAC). See Authentication docs for details. ````