Model Context Protocol
Open JSON-RPC protocol standardizing how LLM applications connect to external tools, data sources, and prompts.
| Version | 2026-07-28 |
|---|---|
| Maturity | stable |
| Owner | w3dev |
| Updated | 2026-08-22 |
| Adopted | 2026-08-22 |
| Tags | ai-agentsprotocolapi |
| Canonical URL | https://modelcontextprotocol.io |
What it is
The Model Context Protocol (MCP) is an open protocol that standardizes how LLM applications (hosts) connect to external context and capabilities through clients and servers, using JSON-RPC 2.0 messages. It defines three roles — hosts (the LLM application), clients (connectors within the host), and servers (services exposing capabilities) — and three core server features: resources (data for the model or user), prompts (templated workflows), and tools (functions the model can invoke). Clients may in turn offer servers elicitation (requesting more information from the user).
MCP is versioned by dated spec revisions; the current revision is
2026-07-28, which introduced a stateless protocol core, multi-round-trip
requests, header-based routing, cacheable list results, authorization
hardening, and a formal extensions framework (e.g. long-running task
extensions, MCP Apps for interactive UI).
Why we adopted this
- One integration surface. Instead of every w3dev tool or data source needing a bespoke integration per AI client, MCP gives us a single protocol that Claude Code, the Claude API, and other MCP-aware clients all speak.
- Decouples tools from models. A server exposing tools/data over MCP works with any conformant client — swapping or adding an AI client doesn't require rewriting the integration.
- Security model built in. The spec bakes in explicit user-consent requirements for data access and tool invocation, which matches how w3dev expects agent tooling to behave by default.
w3dev-specific notes
- Track the dated revision. MCP specs are dated, not semver'd. When we
pin an MCP server or SDK version, record the spec revision it implements
(e.g.
2026-07-28) alongside it, not just a package version. - Prefer Tier 1 SDKs. Use the official SDKs for the language a server is written in rather than hand-rolling JSON-RPC framing.
- Tool descriptions from untrusted servers are untrusted input. Per the spec's trust model, don't let a server's self-reported tool annotations substitute for our own review of what a tool actually does before granting it access to sensitive data.
Links
- Canonical: https://modelcontextprotocol.io
- Current spec revision: https://modelcontextprotocol.io/specification/2026-07-28
- Releases: https://github.com/modelcontextprotocol/modelcontextprotocol/releases