MCP (Model Context Protocol)

OneHazel exposes your workflows to AI assistants — Claude Desktop, Cursor, and any other client that speaks the Model Context Protocol — as callable tools. Your assistant can read what data shapes your workflows accept and run them on demand, without you wiring up a custom backend per assistant.

What is MCP?

MCP is an open standard from Anthropic for connecting AI assistants to external tools and data. A client (Claude Desktop, Cursor, etc.) speaks JSON-RPC 2.0 over HTTP to an MCP server; the server advertises tools, and the client lets the LLM call them when the user asks something that lines up with a tool's purpose.

You can think of it like USB-C for AI assistants: one protocol, many integrations.

How OneHazel fits in

OneHazel hosts a single canonical MCP server URL for every operator:

https://api.onehazel.com/mcp-server

Your API key identifies your operator — the server scopes every request to the operator that owns the key, so you don't paste your operator ID into the URL.

Each of your workflows can be flagged as mcp_exposed in the workflow editor. Exposed workflows become MCP tools — the trigger's effective field schema becomes the tool's inputSchema, and calling the tool runs the workflow end-to-end against your real connections.

Auth is per-API-key: you opt a specific API key into MCP, optionally narrow the allowlist of workflows it can call, and hand that key to your assistant.

Backward compatibility

The legacy per-operator URL https://api.onehazel.com/mcp-server/<your_operator_id> still works. If your assistant is already configured with it, no change is required.

When to use MCP vs. the REST API

You want to…	Use
Let a human (via Claude / Cursor) trigger a workflow in plain English	MCP
Have your own code trigger a workflow on a schedule, on a webhook, or as part of a deterministic pipeline	The REST API and Workflows
Let an AI agent in your own product call workflows	Either — MCP if your agent already speaks it, REST otherwise
Push raw entities / events / states into OneHazel	The Data Ingestion API (MCP is not the right surface for bulk ingestion)

MCP shines when the workflow inputs are small and human-shaped (a customer ID, a date range, a free-text reason) and the workflow itself does real work — calling supplier APIs, transforming data, writing back to your platform.

What's on this page set

• Connecting Claude Desktop — step-by-step setup
• Connecting Cursor — step-by-step setup
• API Reference — initialize, tools/list, tools/call, error codes
• Security — auth model, allowlists, rate limits, audit

Prerequisites

You need an active OneHazel operator account with at least one workflow you want to expose. New to OneHazel? Start with Getting Started and Workflows first.

Protocol version

OneHazel implements MCP protocol version 2025-06-18 (server name onehazel). The server advertises this in its initialize response — see the API Reference.