What is JSON-RPC 2.0?

JSON-RPC 2.0 is a stateless, light-weight remote procedure call (RPC) protocol encoded in JSON. It defines structures for requests, responses, notifications, and errors.

What versions of the Model Context Protocol are supported?

Our parser supports standard JSON-RPC 2.0 structures and checks against MCP specifications including standard tools/call and resources/read schemas.

JSON-RPC 2.0 & MCP Protocol Message Inspector

FmtDev JSON-RPC 2.0 & MCP Protocol Message Inspector is a free, browser-native tool that lets you deep-validate network payloads against official Model Context Protocol specifications. Keep your connection frames private with 100% offline local parsing.

Raw Payload

Protocol Compliance Report

✨ Schema Compliant

Message classified as: Request

PASS

Enter a message and click 'Inspect Message' to start compliance validation.

Engineering Guides

Master This Tool

Deep-dive guides and tutorials for advanced users.

The Developer's Guide to Configuring Custom MCP Servers for Claude & Cursor

Configure custom MCP servers for Claude and Cursor with local-first JSON, stdio transport, and zero-error validation.

Read Guide

The JSON-RPC Renaissance: Protocol Powering 2026 AI Agents

Discover why JSON-RPC 2.0 is the foundational protocol for AI agent tool calling and the Model Context Protocol (MCP) instead of REST or GraphQL.

Read Guide

Understanding MCP Transport Layers: stdio vs. HTTP vs. WebSockets

A technical deep dive into Model Context Protocol (MCP) transport mechanisms. Compare stdio, HTTP with SSE, and WebSockets for secure AI agent integration.

Read Guide