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HomeDocsModel Context Protocol 28 Sep 2026
One change · mcp

Streamable HTTP changedspecification/draft/basic/transports/streamable-http

Nearest release: v2.1.284, published 4 hours before upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Upstream edited this page at 28 Sep 2026 21:57 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 28 Sep 2026 22:07 UTC.

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Lines−19removed
From line 282 where the diff opens
First seen 26 Aug 2026 this site's first read of the page
Recorded edits3to this page, all time

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282282 
283283### Standard Request Headers
284284 
285| Header Name | Source Field | Required For |
286| ------------ | ----------------------------- | ------------------------------------------------------ |
287| `Mcp-Method` | `method` | All requests |
288| `Mcp-Name` | `params.name` or `params.uri` | `tools/call`, `resources/read`, `prompts/get` requests |
285| Header Name | Source Field | Required For |
286| - | - | - |
287| `Mcp-Method` | `method` | All requests |
288| `Mcp-Name` | `params.name` or `params.uri` | `tools/call`, `resources/read`, `prompts/get` requests |
289289 
290290These headers are **REQUIRED** for compliance.
291291 
from line 507
507507 
508508**Encoding examples:**
509509 
510| Original Value | Reason | Encoded Header Value |
511| ---------------------- | ------------------------ | ----------------------------------------------------- |
512| `"us-west1"` | Plain ASCII | `Mcp-Param-Region: us-west1` |
513| `"Hello, 世界"` | Contains non-ASCII | `Mcp-Param-Greeting: =?base64?SGVsbG8sIOS4lueVjA==?=` |
514| `" padded "` | Leading/trailing spaces | `Mcp-Param-Text: =?base64?IHBhZGRlZCA=?=` |
515| `"line1\nline2"` | Contains newline | `Mcp-Param-Text: =?base64?bGluZTEKbGluZTI=?=` |
516| `"=?base64?literal?="` | Matches sentinel pattern | `Mcp-Param-Val: =?base64?PT9iYXNlNjQ/bGl0ZXJhbD89?=` |
510| Original Value | Reason | Encoded Header Value |
511| - | - | - |
512| `"us-west1"` | Plain ASCII | `Mcp-Param-Region: us-west1` |
513| `"Hello, 世界"` | Contains non-ASCII | `Mcp-Param-Greeting: =?base64?SGVsbG8sIOS4lueVjA==?=` |
514| `" padded "` | Leading/trailing spaces | `Mcp-Param-Text: =?base64?IHBhZGRlZCA=?=` |
515| `"line1\nline2"` | Contains newline | `Mcp-Param-Text: =?base64?bGluZTEKbGluZTI=?=` |
516| `"=?base64?literal?="` | Matches sentinel pattern | `Mcp-Param-Val: =?base64?PT9iYXNlNjQ/bGl0ZXJhbD89?=` |
517517 
518518[rfc9110-values]: https://datatracker.ietf.org/doc/html/rfc9110#name-field-values
519519 
from line 556
556556`400 Bad Request` HTTP status and JSON-RPC error code `-32020`
557557(`HeaderMismatch`) if any validation fails.
558558 
559| Scenario | Client Behavior | Server Behavior |
560| ---------------------------------------- | ------------------------------ | ---------------------------------------- |
561| Parameter value provided | Client MUST include the header | Server MUST validate header matches body |
562| Parameter value is `null` | Client MUST omit the header | Server MUST NOT expect the header |
563| Parameter not in arguments | Client MUST omit the header | Server MUST NOT expect the header |
564| Client omits header but value is in body | Non-conforming client | Server MUST reject the request |
559| Scenario | Client Behavior | Server Behavior |
560| - | - | - |
561| Parameter value provided | Client MUST include the header | Server MUST validate header matches body |
562| Parameter value is `null` | Client MUST omit the header | Server MUST NOT expect the header |
563| Parameter not in arguments | Client MUST omit the header | Server MUST NOT expect the header |
564| Client omits header but value is in body | Non-conforming client | Server MUST reject the request |
565565 
566566[http-semantics]: https://www.rfc-editor.org/rfc/rfc9110.html#name-field-names
567567 
from line 594
594594return HTTP status `400 Bad Request` and **MUST** include a JSON-RPC error
595595response using the following error code:
596596 
597| Code | Name | Description |
598| -------- | ------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
597| Code | Name | Description |
598| - | - | - |
599599| `-32020` | [`HeaderMismatch`](/specification/draft/schema#headermismatcherror) | The HTTP headers do not match the corresponding values in the request body, or required headers are missing/malformed. |
600600 
601601This error code is allocated from the sub-range the MCP specification
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