MCP Architecture: How Lexera Speaks JSON-RPC Over SSE

Lexera exposes its legal verification pipeline through the Model Context Protocol (MCP), an open standard that lets AI agents and enterprise systems call tools over a persistent, event-driven transport. Because human attorney review takes time, Lexera’s implementation is fully asynchronous and stateful: you open a single long-lived connection, dispatch a request, and receive the result later as a server event.

Why JSON-RPC 2.0 over SSE

Traditional REST APIs expect an immediate response, which does not fit a workflow where a law firm may spend hours reviewing a contract. Lexera solves this with Server-Sent Events (SSE): a persistent HTTP connection that the server uses to push status updates, results, and errors back to your system. JSON-RPC 2.0 provides a lightweight, structured message format for invoking tools and correlating responses.

JSON-RPC 2.0 message format

Every tool call is a JSON-RPC 2.0 request. The envelope is predictable and easy to generate from any language.

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "lexera_route_to_specialist",
    "arguments": {
      "document_text": "Vendor contract with uncapped liability clause...",
      "target_jurisdiction": "UAE",
      "specialist_instructions": "Cap liability at 100% of contract value."
    }
  }
}

Field	Description
`jsonrpc`	Must be exactly `"2.0"`.
`id`	A client-generated identifier used to match responses.
`method`	Always `"tools/call"` for Lexera MCP tool invocation.
`params.name`	The MCP tool name (for example, `lexera_route_to_specialist`).
`params.arguments`	Tool-specific parameters documented on each tool’s reference page.

Server-Sent Events transport

Lexera streams three kinds of information over SSE:

Session initialization — After you open the stream, the server sends an event: endpoint containing your unique session URL. You must extract this URL to dispatch any RPC.
Execution results — Once you POST a tool call, the eventual result (for example, DISPATCH_SUCCESS or a completed order payload) arrives as a later SSE message on the same connection.
Errors — Validation failures, wallet issues, and authentication problems are also streamed as JSON-RPC error payloads over SSE.

The `event: endpoint` handshake

Immediately after opening the SSE stream, the server pushes a session assignment. The event looks like this:

event: endpoint
data: /mcp-server/messages?sessionId=550e8400-e29b-41d4-a716-446655440000

Your code must parse the data line, prepend https://lexera.dev, and use the resulting URL for every subsequent JSON-RPC POST. Without this step, the server cannot correlate your tool calls with your open stream.

All SSE traffic, including the initial session assignment, requires a valid Bearer token. See Authentication for how to obtain and pass your API key.

Next steps

Learn the exact three-step flow in Execution Lifecycle
See the full list of available MCP tools in Tools Overview

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Core Concepts

Guides

MCP Architecture: How Lexera Speaks JSON-RPC Over SSE

Why JSON-RPC 2.0 over SSE

JSON-RPC 2.0 message format

Server-Sent Events transport

The `event: endpoint` handshake

Next steps

​Why JSON-RPC 2.0 over SSE

​JSON-RPC 2.0 message format

​Server-Sent Events transport

​The event: endpoint handshake

​Next steps

Why JSON-RPC 2.0 over SSE

JSON-RPC 2.0 message format

Server-Sent Events transport

The `event: endpoint` handshake

Next steps