189 pages for compatibility.

SEP-1036: URL Mode Elicitation for secure out-of-band interactions Model Context Protocol · in the page seps/1036-url-mode-elicitation-for-secure-out-of-band-intera …": { "form": {}, "url": {} } } } ``` For backwards compatibility, an empty capabilities object is equivalent to declaring support for `form` mode only: ```jsonc theme={null} { "c… SEP-1046: Support OAuth client credentials flow in authorization Model Context Protocol · in the page seps/1046-support-oauth-client-credentials-flow-in-authoriza …2. Client Secrets via HTTP Basic authentication (Allowed for maximum compatibility with existing systems) Other options, such as mTLS, are not included. While the spec encourages the use of RFC 752… SEP-1302: Formalize Working Groups and Interest Groups in MCP Governance Model Context Protocol · in the page seps/1302-formalize-working-groups-and-interest-groups-in-mc …level; we need a centralized point of discernment here. ## Backward Compatibility *All SEPs that introduce backward incompatibilities must include a section describing these incompatibilities and t… SEP-1303: Input Validation Errors as Tool Execution Errors Model Context Protocol · in the page seps/1303-input-validation-errors-as-tool-execution-errors …rtureDate: "12/12/2025" // Future date } } } ``` ## Backwards Compatibility This change is backwards compatible as it: * Does not alter the protocol structure * Only clarifies existing ambig… SEP-1319: Decouple Request Payload from RPC Methods Definition Model Context Protocol · in the page seps/1319-decouple-request-payload-from-rpc-methods-definiti …future growth without penalizing the current ecosystem. ## Backward Compatibility This proposal is a **non-breaking change** for existing implementations. It is a refactoring of the *specification… SEP-1330: Elicitation Enum Schema Improvements and Standards Compliance Model Context Protocol · in the page seps/1330-elicitation-enum-schema-improvements-and-standards …https://github.com/evalstate/fast-agent/pull/324/files) ## Backwards Compatibility The `LegacyEnumSchema` type maintains backwards compatible during the migration period. Existing implementations us… SEP-1577: Sampling With Tools Model Context Protocol · in the page seps/1577--sampling-with-tools …ED [key: string]: unknown; } ``` * Notes: * Backwards compatibility issue: returning CreateMessageResult.content as an array of contents OR a single content is problematic, so we propo… SEP-1613: Establish JSON Schema 2020-12 as Default Dialect for MCP Model Context Protocol · in the page seps/1613-establish-json-schema-2020-12-as-default-dialect-f …ects via the `$schema` field. This resolves ambiguity that has caused compatibility issues between implementations. ## Motivation The MCP specification does not explicitly state which JSON Schema ve… SEP-1686: Tasks Model Context Protocol · in the page seps/1686-tasks …on-related information. This approach also provides natural backward compatibility. Servers that don't support tasks can ignore the `_meta` content without breaking request processing. The request pa… SEP-1699: Support SSE polling via server-side disconnect Model Context Protocol · in the page seps/1699-support-sse-polling-via-server-side-disconnect …ing the server with inappropriate reconnection attempts. ## Backward Compatibility * **New Client + Old Server**: No changes. No backward incompatibility. * **Old Client + New Server**: Client shoul… SEP-1730: SDKs Tiering System Model Context Protocol · in the page seps/1730-sdks-tiering-system …** Current ad-hoc approach creates uncertainty for users ## Backward Compatibility This proposal introduces a new classification system with no breaking changes: * Existing SDKs continue to functio… SEP-1850: PR-Based SEP Workflow Model Context Protocol · in the page seps/1850-pr-based-sep-workflow …Abstract ## Motivation ## Specification ## Rationale ## Backward Compatibility ## Security Implications ## Reference Implementation ``` ### 7. Status Management via PR Labels To improve disco… SEP-1865: MCP Apps - Interactive User Interfaces for MCP Model Context Protocol · in the page seps/1865-mcp-apps-interactive-user-interfaces-for-mcp …orted with the SEP's new `externalIframes` capability. ## Backward Compatibility The proposal is an optional extension to the core protocol. Existing implementations continue working without chang… SEP-2085: Governance Succession and Amendment Procedures Model Context Protocol · in the page seps/2085-governance-succession-and-amendment …least one meeting cycle while enabling timely decisions. ## Backward Compatibility This SEP adds new procedures without modifying existing governance structures. No backward compatibility concerns e… SEP-2106: Tools `inputSchema` & `outputSchema` Conform to JSON Schema 2020-12 Model Context Protocol · in the page seps/2106-json-schema-2020-12 …the expressiveness of JSON Schema 2020-12 while maintaining backward compatibility with existing implementations. ## Motivation The current MCP specification restricts tool schemas in ways that con… SEP-2127: MCP Server Cards - HTTP Server Discovery Model Context Protocol · in the page seps/2127-mcp-server-cards …may evolve the specification independently while preserving backward compatibility; breaking changes require a new extension identifier. At a high level, the Server Card extension introduces: * **S… SEP-2133: Extensions Model Context Protocol · in the page seps/2133-extensions …loyed at any time, but changes MUST ensure they account for backwards compatibility in their design. #### Promotion to Core Protocol (Optional) Eventually, some extensions MAY transition to being co… SEP-2148: MCP Contributor Ladder Model Context Protocol · in the page seps/2148-contributor-ladder …elines) authorship or co-authorship * Protocol design participation * Compatibility analysis #### Documentation * User guides and tutorials * API documentation * Architecture documentation * Maintai… SEP-2149: MCP Group Governance and Charter Template Model Context Protocol · in the page seps/2149-working-group-charter-template …d cloud deployments—while maintaining protocol coherence and backward compatibility. *IG Example:* > The Enterprise IG explores the challenges of deploying MCP in enterprise environments, gathering… SEP-2164: Standardize Resource Not Found Error Code Model Context Protocol · in the page seps/2164-resource-not-found-error …ning and is universally understood by JSON-RPC libraries ## Backward Compatibility This changes what is specified — the current spec recommends `-32002`, and this SEP changes it to `-32602`. However… SEP-2207: OIDC-Flavored Refresh Token Guidance Model Context Protocol · in the page seps/2207-oidc-refresh-token-guidance …n OAuth and OIDC specs for this guidance as it can vary. ## Backward Compatibility This proposal is fully backward-compatible: * Clients that already request `offline_access` continue to work * Aut… SEP-2243: HTTP Header Standardization for Streamable HTTP Transport Model Context Protocol · in the page seps/2243-http-standardization …: Easier to support multiple MCP versions in clients and servers 3. **Compatibility**: Headers work with the existing Streamable HTTP transport design without changing the endpoint structure 4. **Unli… SEP-2260: Require Server requests to be associated with a Client request. Model Context Protocol · in the page seps/2260-Require-Server-requests-to-be-associated-with-Client-requests …quests **MUST NOT** be + sent on standalone streams. ``` ## Backward Compatibility ### Impact Assessment This change is expected to have **minimal to no impact** on existing implementations: 1. **… SEP-2322: Multi Round-Trip Requests Model Context Protocol · in the page seps/2322-MRTR …the Client should assume a `ResultType` of `"complete"` for backwards compatibility. Extensions **MAY** add additional `ResultType` values. The set of supported `ResultType` values **MUST** be create… SEP-2468: Recommend Issuer (iss) Parameter in MCP Auth Responses Model Context Protocol · in the page seps/2468-recommend-issuer-claim-for-auth …would reject legitimate flows without security benefit. ## Backward Compatibility The `iss` parameter is additive on the wire. Client validation introduces a behavioral change for hosts whose autho… SEP-2484: Require Conformance Tests for Standards Track SEPs to Reach Final Status Model Context Protocol · in the page seps/2484-conformance-tests-required-for-final-seps …e sponsor verify completeness without reading test code. ## Backward Compatibility This SEP is **not retroactive**. SEPs that reached `Final` before this SEP takes effect are not required to add con… SEP-2549: TTL for List Results Model Context Protocol · in the page seps/2549-TTL-for-list-results …also be treated as `"private"`. ### Error handling * For backwards compatibility, If `ttlMs` is missing, clients SHOULD assume a default `ttlMs` of `0` (immediately stale) and rely on their own cac… SEP-2567: Sessionless MCP via Explicit State Handles Model Context Protocol · in the page seps/2567-sessionless-mcp …s a designed replacement rather than a mechanical edit; see [Backward Compatibility](#backward-compatibility). ## Backward Compatibility This is a **breaking change** for servers that rely on protoc… SEP-2575: Make MCP Stateless Model Context Protocol · in the page seps/2575-stateless-mcp …o making it more flexible and extensible for the future. ## Backward Compatibility While this proposal attempts to preserve existing functionality and use-cases, this proposal introduces a **fundame… SEP-2577: Deprecate Roots, Sampling, and Logging Model Context Protocol · in the page seps/2577-deprecate-roots-sampling-and-logging …NOT add support for deprecated features unless needed for backward compatibility with existing counterparts. ### Timeline * **Deprecated**: In the next specification release (currently planned fo… SEP-2596: Specification Feature Lifecycle and Deprecation Policy Model Context Protocol · in the page seps/2596-spec-feature-lifecycle-and-deprecation …port is described as "deprecated" in the [Streamable HTTP backwards-compatibility guidance][transports-compat], with no stated removal date. * The `includeContext` values `"thisServer"` and `"allS… SEP-2640: Skills Extension Model Context Protocol · in the page seps/2640-skills-extension …ges in a backwards incompatible way, clients MUST honor any backwards compatibility mechanisms provided by the Agent Skills specification and SHOULD continue to support the Agent Skills specification… SEP-2663: Tasks Extension Model Context Protocol · in the page seps/2663-tasks-extension …Clients do not need to deduplicate across the two flows. ## Backward Compatibility The experimental tasks feature in the `2025-11-25` release is **not wire-compatible** with this extension. Implemen… SEP-414: Document OpenTelemetry Trace Context Propagation Conventions Model Context Protocol · in the page seps/414-request-meta …this SEP for forwarding `_meta` values to HTTP headers ## Backward Compatibility This SEP documents existing conventions and is backward compatible. ## Security Implications Trace context in `_m… SEP-932: Model Context Protocol Governance Model Context Protocol · in the page seps/932-model-context-protocol-governance …e Core Maintainers * Admin access to all infrastructure ## Backwards Compatibility N/A ## Reference Implementation See #931 1. **Documentation Files**: * `/docs/community/governance.mdx` - Ful… SEP-973: Expose additional metadata for Implementations, Resources, Tools and Prompts Model Context Protocol · in the page seps/973-expose-additional-metadata-for-implementations-res …he following MIME types: * - image/png - PNG images (safe, universal compatibility) * - image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility) * * Clients that support rendering… SEP-985: Align OAuth 2.0 Protected Resource Metadata with RFC 9728 Model Context Protocol · in the page seps/985-align-oauth-20-protected-resource-metadata-with-rf …er C,M: MCP communication continues with valid token ``` ## Backward Compatibility This proposal is fully backward-compatible. It retains support for the WWW-Authenticate header (already in the spe… SEP-986: Specify Format for Tool Names Model Context Protocol · in the page seps/986-specify-format-for-tool-names …dashes (-), dots (.), and forward slashes (/). This aims to maximize compatibility, clarity, and interoperability across MCP implementations while accommodating a wide range of naming conventions. #… SEP-991: Enable URL-based Client Registration using OAuth Client ID Metadata Documents Model Context Protocol · in the page seps/991-enable-url-based-client-registration-using-oauth-c …developers succeed in following the specification, and the promise of compatibility and an open ecosystem suffers as a result. This proposal intends to simplify the story for authorization server and… SEP-994: Shared Communication Practices/Guidelines Model Context Protocol · in the page seps/994-shared-communication-practicesguidelines …ents**: Ensures decisions are preserved and discoverable ## Backward Compatibility This SEP establishes new processes and does not affect existing protocol functionality. ## Reference Implementatio… Architecture Model Context Protocol · in the page specification/2024-11-05/architecture/index …dently * Protocol designed for future extensibility * Backwards compatibility is maintained ## Message Types MCP defines three core message types based on [JSON-RPC 2.0](https://www.jsonrpc.or… Lifecycle Model Context Protocol · in the page specification/2024-11-05/basic/lifecycle …ring this phase, the client and server: * Establish protocol version compatibility * Exchange and negotiate capabilities * Share implementation details The client **MUST** initiate this phase by sen… Architecture Model Context Protocol · in the page specification/2025-03-26/architecture/index …dently * Protocol designed for future extensibility * Backwards compatibility is maintained ## Capability Negotiation The Model Context Protocol uses a capability-based negotiation system wher… Lifecycle Model Context Protocol · in the page specification/2025-03-26/basic/lifecycle …ring this phase, the client and server: * Establish protocol version compatibility * Exchange and negotiate capabilities * Share implementation details The client **MUST** initiate this phase by sen… Transports Model Context Protocol · in the page specification/2025-03-26/basic/transports …http-with-sse) from > protocol version 2024-11-05. See the [backwards compatibility](#backwards-compatibility) > guide below. In the **Streamable HTTP** transport, the server operates as an independe… Architecture Model Context Protocol · in the page specification/2025-06-18/architecture/index …dently * Protocol designed for future extensibility * Backwards compatibility is maintained ## Capability Negotiation The Model Context Protocol uses a capability-based negotiation system wher… Lifecycle Model Context Protocol · in the page specification/2025-06-18/basic/lifecycle …ring this phase, the client and server: * Establish protocol version compatibility * Exchange and negotiate capabilities * Share implementation details The client **MUST** initiate this phase by sen… Transports Model Context Protocol · in the page specification/2025-06-18/basic/transports …http-with-sse) from > protocol version 2024-11-05. See the [backwards compatibility](#backwards-compatibility) > guide below. In the **Streamable HTTP** transport, the server operates as an independe… Tools Model Context Protocol · in the page specification/2025-06-18/server/tools …N object in the `structuredContent` field of a result. For backwards compatibility, a tool that returns structured content SHOULD also return the serialized JSON in a TextContent block. > [!NOTE] >… Architecture Model Context Protocol · in the page specification/2025-11-25/architecture/index …dently * Protocol designed for future extensibility * Backwards compatibility is maintained ## Capability Negotiation The Model Context Protocol uses a capability-based negotiation system wher…