Follow Discord
Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
HomeDocsModel Context Protocol 28 Sep 2026
One change · mcp

Overview changedspecification/2026-07-28/basic/index

Nearest release: v2.1.284, published 4 hours before this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Recorded here
Lines+22added
Lines−22removed
From line 126 where the diff opens
First seen 14 Aug 2026 this site's first read of the page
Recorded edits3to this page, all time

The whole hunk

from line 126, old and new numbered
/
lines
from line 126
126126 
127127MCP defines the following error codes:
128128 
129| Code | Name |
130| -------- | ---------------------------------------------------------------------------------------------------------- |
131| `-32020` | [`HeaderMismatch`](/specification/2026-07-28/schema#headermismatcherror) |
129| Code | Name |
130| - | - |
131| `-32020` | [`HeaderMismatch`](/specification/2026-07-28/schema#headermismatcherror) |
132132| `-32021` | [`MissingRequiredClientCapability`](/specification/2026-07-28/schema#missingrequiredclientcapabilityerror) |
133| `-32022` | [`UnsupportedProtocolVersion`](/specification/2026-07-28/schema#unsupportedprotocolversionerror) |
133| `-32022` | [`UnsupportedProtocolVersion`](/specification/2026-07-28/schema#unsupportedprotocolversionerror) |
134134 
135135Codes defined by earlier protocol versions remain reserved and will not be
136136reused. Implementations of this protocol version **MUST NOT** emit these codes:
from line 345
345345 
346346The following `_meta` keys are reserved by this specification:
347347 
348| Key | Description | Defined in |
349| -------------------------------------------- | ----------------------------------------------------------- | ----------------------------------------------------------------------- |
350| `progressToken` | Opts the request into progress notifications | [Progress](/specification/2026-07-28/basic/patterns/progress) |
351| `io.modelcontextprotocol/protocolVersion` | Protocol version for a request | Per-request protocol fields (below) |
352| `io.modelcontextprotocol/clientInfo` | Client name and version | Per-request protocol fields (below) |
353| `io.modelcontextprotocol/clientCapabilities` | Client capabilities relevant to a request | Per-request protocol fields (below) |
354| `io.modelcontextprotocol/logLevel` | Minimum log level the server should emit for a request | [Logging](/specification/2026-07-28/server/utilities/logging) |
355| `io.modelcontextprotocol/subscriptionId` | Correlates a notification with its originating subscription | [Subscriptions](/specification/2026-07-28/basic/patterns/subscriptions) |
356| `traceparent`, `tracestate`, `baggage` | OpenTelemetry trace context propagation | OpenTelemetry trace context (below) |
348| Key | Description | Defined in |
349| - | - | - |
350| `progressToken` | Opts the request into progress notifications | [Progress](/specification/2026-07-28/basic/patterns/progress) |
351| `io.modelcontextprotocol/protocolVersion` | Protocol version for a request | Per-request protocol fields (below) |
352| `io.modelcontextprotocol/clientInfo` | Client name and version | Per-request protocol fields (below) |
353| `io.modelcontextprotocol/clientCapabilities` | Client capabilities relevant to a request | Per-request protocol fields (below) |
354| `io.modelcontextprotocol/logLevel` | Minimum log level the server should emit for a request | [Logging](/specification/2026-07-28/server/utilities/logging) |
355| `io.modelcontextprotocol/subscriptionId` | Correlates a notification with its originating subscription | [Subscriptions](/specification/2026-07-28/basic/patterns/subscriptions) |
356| `traceparent`, `tracestate`, `baggage` | OpenTelemetry trace context propagation | OpenTelemetry trace context (below) |
357357 
358358Official [extensions](/specification/2026-07-28/basic/versioning#extension-negotiation)
359359define additional `_meta` keys under the `io.modelcontextprotocol/` prefix, and
from line 368
368368prior connection state. See
369369[Versioning and Compatibility][lifecycle] for version negotiation rules.
370370 
371| Key | Type | Required | Description |
372| -------------------------------------------- | -------------------- | -------- | --------------------------------------------------------- |
373| `io.modelcontextprotocol/protocolVersion` | `string` | Yes | Protocol version for this request (e.g., `"2026-07-28"`) |
374| `io.modelcontextprotocol/clientInfo` | `Implementation` | No | Client name and version |
375| `io.modelcontextprotocol/clientCapabilities` | `ClientCapabilities` | Yes | Client capabilities relevant to this request |
376| `io.modelcontextprotocol/logLevel` | `LoggingLevel` | No | Minimum log level the server should emit for this request |
371| Key | Type | Required | Description |
372| - | - | - | - |
373| `io.modelcontextprotocol/protocolVersion` | `string` | Yes | Protocol version for this request (e.g., `"2026-07-28"`) |
374| `io.modelcontextprotocol/clientInfo` | `Implementation` | No | Client name and version |
375| `io.modelcontextprotocol/clientCapabilities` | `ClientCapabilities` | Yes | Client capabilities relevant to this request |
376| `io.modelcontextprotocol/logLevel` | `LoggingLevel` | No | Minimum log level the server should emit for this request |
377377 
378378A request missing any required field is malformed; the server **MUST** reject it with
379379JSON-RPC error code `-32602` (Invalid params). On HTTP, the response status **MUST** be
from line 395
395395every result's `_meta`, unless specifically configured not to do so, to
396396identify themselves without relying on any prior connection state:
397397 
398| Key | Type | Required | Description |
399| ------------------------------------ | ---------------- | -------- | ----------------------- |
400| `io.modelcontextprotocol/serverInfo` | `Implementation` | No | Server name and version |
398| Key | Type | Required | Description |
399| - | - | - | - |
400| `io.modelcontextprotocol/serverInfo` | `Implementation` | No | Server name and version |
401401 
402402<Note>
403403 `io.modelcontextprotocol/clientInfo` and `io.modelcontextprotocol/serverInfo`
Feedback