Glossary - ChristianPresley/zig-sdk GitHub Wiki
This page defines the terms the wiki uses. The Dictionary lists the approved technical words. The specification defines the protocol terms1.
Applies to: MCP 2026-07-28, zig-sdk 0.1.0. The terms of the features that version 0.2.0 added apply to zig-sdk 0.2.0.
| Term | Meaning |
|---|---|
| Arena | An allocator that frees all its memory at once. Every request has one. |
| Authorization server | The server that issues access tokens for MCP servers. The SDK has one in mcp.auth.AuthorizationServer. |
| Capability | A feature that a client or a server declares. |
| Challenge | A 401 or 403 response with a WWW-Authenticate header. |
| Client | The program that sends requests to a server. |
| Client credentials | An OAuth grant for a machine client without a user. The client gets a token with its own credentials. |
| Conformance suite | The official test suite of the MCP project. |
| Cursor | An opaque value in a list result that selects the next page. |
| Custom transport | A transport that the specification does not define, such as the gRPC binding. It keeps the JSON-RPC messages and the request patterns. |
| Discovery | The server/discover request, or the metadata lookups of authorization. |
| DPoP | Proof of possession at the application layer (RFC 9449). A DPoP-bound token is valid only with a proof that the key of the client signs. |
| Enterprise identity provider (IdP) | The service that signs in the users of an organization and decides which MCP servers they can use. |
| Extension | An optional part of the protocol with its own identifier, such as the Tasks, Skills or Apps extension. |
| Frame | One serialized JSON-RPC message. |
| Handler | A Zig function that answers a request. |
| Header mirroring | The copy of the method, the name and the annotated parameters of a request into HTTP headers or gRPC metadata. |
| Hook | A Zig function that a client calls to answer an input request. |
| Host | The application that owns clients. |
| Hybrid key exchange | A TLS key exchange that joins a post-quantum KEM and a classical group, such as X25519MLKEM768. An attacker must break both parts. |
| Icon | An image that a server attaches to its implementation, tools, resources, resource templates or prompts. The client fetches it under the icon rules. |
| ID-JAG | Identity Assertion JWT Authorization Grant. A JWT from the IdP that the client gives to the authorization server of an MCP server for an access token. |
| Input request | A request for elicitation, sampling or roots inside an input_required result. |
| Issuer | The identifier of an authorization server. |
| Job object | A Windows object that holds a process tree. The stdio client ends the tree through it. |
| Keychain | The credential store of the host: the Credential Manager on Windows, Keychain Services on macOS and the Secret Service on Linux. |
| KEM | Key encapsulation mechanism. One side encapsulates a secret with the public key of the other side, and the other side decapsulates it. ML-KEM-768 is a KEM. |
| Listen stream | The long-lived subscriptions/listen request. |
| Multi round-trip request (MRTR) | A request that the client sends again with the answers to input requests. |
| Origin | The scheme, the host and the port of a URL. The client fetches https icons from the origin of the server only, unless the policy trusts other origins. |
| Principal | The identity that a resource server gets from a valid access token. A handler reads it from the request context. |
| Process group | A POSIX group of processes that get the same signal. The stdio client ends the server tree through it. |
| Prompt | A template for a model message. |
| Regular expression | A pattern for strings. The JSON Schema keywords pattern and patternProperties contain regular expressions in the ECMA-262 syntax. |
| Request state | The opaque value a server gives with an input_required result and the client echoes. |
| Resource | Data with a URI that a server exposes. |
| Resource template | A URI template that names a family of resources. |
| Reverse proxy | A server that receives the requests of clients and forwards them to the SDK server. |
| Revision | A dated version of the specification, such as 2026-07-28. |
| RSA-PSS | The RSA signature scheme with a random salt. The TLS server and the TLS client sign with it when their key is an RSA key. |
| Sentinel | The =?base64?...?= form of a header value. |
| Server | The program that answers requests. |
| Server-sent events (SSE) | A stream of events in one HTTP response with the type text/event-stream. |
| Skill | A directory of files with a SKILL.md file at its root. A server publishes skills with the Skills extension. |
| Skill entry | The data of one skill in skills/list: the URI of SKILL.md, the frontmatter, and the digest and the size of each file. |
| Task | A tool call that continues after its request ended. The Tasks extension defines it. |
| Template variable | A named part of a URI template, such as id in users://{id}/profile. |
| Token storage | The place where an OAuth client keeps its registration and its tokens for the next process: memory, encrypted files or the keychain. |
| Token exchange | An OAuth grant that changes one token into a token of another type, such as an ID token into an ID-JAG. |
| Tool | A function that a model can call through a server. |
| Transport | The binding that carries frames: stdio, Streamable HTTP, HTTPS, gRPC, WebSocket or a Unix domain socket. |
| Tunnel | The gRPC service of the SDK in proto/mcp_zig_transport_v1.proto. Each gRPC message carries one JSON-RPC message. |
| Typed binding | The gRPC service model_context_protocol.Mcp of the Google Cloud proto files. Each RPC carries one MCP request as typed protobuf messages. |
| Unix domain socket | A socket at a file system path that connects processes on the same computer. |
| URI template | A pattern for URIs with variables in braces. The SDK supports a subset of RFC 6570. |
| View | An HTML document in a ui:// resource that a host shows in a sandboxed frame. The Apps extension defines it. Also called a UI resource. |
| WebSocket | A protocol for messages in the two directions on one connection (RFC 6455). The WebSocket transport uses the subprotocol mcp. |
- MCP-ARCH-2026-07-28: Architecture of the protocol.