Agents & tools · Glossary term
What is Multi Round-Trip Request (MRTR)?
An MCP request pattern in which an operation returns `resultType: input_required` with one or more `inputRequests`, then the client retries the original method with `inputResponses` and the exact returned `requestState`.
Also called MRTR.
Why does Multi Round-Trip Request (MRTR) matter?
It lets a stateless server request user, model, or root input without opening a server-initiated JSON-RPC exchange or storing protocol session state.
Multi Round-Trip Request (MRTR) in practice
Return an input request from `tools/call`, collect the authorized response in the host, and retry that same tool call with a new JSON-RPC id.
What is the common confusion about Multi Round-Trip Request (MRTR)?
`requestState` is untrusted round-trip data. Integrity-protect it before using it for authorization or business decisions, and do not treat it as a server-side session identifier.
Learn Multi Round-Trip Request (MRTR) in the course
Start with
- Explicit Scope and Stateless Elicitation
Roots are deprecated in MCP 2026-07-28 and were never a security sandbox. Put scope in visible tool arguments or resource URIs, authorize it on the server, and use MRTR when a tool genuinely needs…
Lessons that name Multi Round-Trip Request (MRTR) in a title or section
- MCP Model Input: Sampling Migration and Stateless MRTR
MCP 2026-07-28 deprecates Sampling for new designs and removes the server-to-client request channel. If an existing workflow still needs the client's model, the server returns an inputrequired…
- MCP Security: Poisoned Metadata, Routing, and MRTR State
Stateless does not mean trustless. It means every request exposes the evidence a server and gateway need to validate the call independently.
- Stateless MCP Gateways and Registry Admission
A gateway should make every route explicit. The 2026-07-28 protocol gives it method, name, version, capability, identity, cache, and trace boundaries without a transport session.
Taught in Phase 13: Tools & Protocols.
Related terms
- Stateless MCPThe MCP 2026-07-28 request model in which every request carries the protocol version and client capabilities in `params._meta`, while…
- MCP (Model Context Protocol)An open JSON-RPC protocol for a host to connect to servers that expose tools, resources, prompts, and extensions through defined request,…
- Human-in-the-Loop (HITL)A workflow design in which a person supplies judgment, correction, approval, or escalation at defined points in an AI-driven process.
- Tool ContractThe complete agreement for a tool boundary: purpose, typed inputs, outputs, validation, permissions, side effects, errors, timeouts,…
Sources
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This entry comes from glossary/terms.md on GitHub. Browse all 250 glossary terms.