MCP concepts
MCP News documents 4 MCP concepts - protocol terms like the stateless core, MRTR, and tool poisoning - each defined factually with a citation into the spec or an authoritative source.
- Multi Round-Trip Requests (MRTR) - protocol
The 2026-07-28 pattern that replaces server-initiated requests (elicitation/create, sampling/createMessage, roots/list): when a request needs more input mid-call, the server returns a result with resultType "input_required" carrying the requests it needs answered, and the client retries the original call with the answers attached in inputResponses.
- Stateless core - protocol
The 2026-07-28 revision's redesign of MCP from a bidirectional stateful protocol into a request/response stateless one: the initialize handshake and protocol-level session are removed, every request carries its protocol version, client identity, and capabilities in _meta, and any request can land on any server instance behind a plain load balancer.
- Streamable HTTP - transport
MCP's HTTP transport, introduced in the 2025-03-26 revision as the replacement for the original HTTP+SSE transport. A single endpoint accepts JSON-RPC POST requests; since 2026-07-28, requests must carry the Mcp-Method and Mcp-Name headers for header-based routing, and the legacy HTTP+SSE transport is formally deprecated.
- Tool poisoning - security
An indirect prompt injection attack against MCP-connected agents: a malicious server returns tool descriptions or tool responses containing hidden instructions, which the model treats as trusted context and may follow - calling restricted tools, leaking data, or bypassing its system prompt. OWASP documents the root cause as a trust gap between connect-time review and unvalidated runtime responses.