Enum ProtocolVersion 

pub enum ProtocolVersion {
    V2024_11_05,
    V2025_03_26,
    V2025_06_18,
    V2025_11_25,
}

MCP protocol versions in chronological order.

The ordering is: V2024_11_05 < V2025_03_26 < V2025_06_18 < V2025_11_25

This enum implements Ord, so you can compare versions:

use mcpkit_core::protocol_version::ProtocolVersion;

assert!(ProtocolVersion::V2025_11_25 > ProtocolVersion::V2024_11_05);
assert!(ProtocolVersion::V2025_03_26 >= ProtocolVersion::V2024_11_05);

Variants

V2024_11_05

Original MCP specification (November 2024).

Features: HTTP+SSE transport, tools, resources, prompts.

V2025_03_26

OAuth 2.1 and Streamable HTTP update (March 2025).

New features:

• OAuth 2.1 authorization framework
• Streamable HTTP transport (replaces HTTP+SSE)
• JSON-RPC batching (removed in 2025-06-18)
• Tool annotations (readOnly, destructive)
• Audio content type
• Completions capability

V2025_06_18

Security and elicitation update (June 2025).

New features:

• Elicitation (server requesting user input)
• Structured tool output
• Resource links in tool results
• Protected resource metadata
• _meta field in messages
• title field for display names

Breaking changes:

• Removed JSON-RPC batching
• MCP-Protocol-Version header required

V2025_11_25

Tasks and parallel tools update (November 2025).

New features:

• Tasks with async status tracking
• Parallel tool calls
• Server-side agent loops
• Tool calling in sampling requests

Implementations

impl ProtocolVersion

pub const LATEST: Self = Self::V2025_11_25

The latest supported protocol version.

pub const DEFAULT: Self = Self::LATEST

The default version used when not specified.

pub const ALL: &'static [Self]

All supported versions in chronological order.

pub const fn as_str(&self) -> &'static str

Returns the string representation used in the protocol.

This matches the format expected in MCP messages (e.g., "2025-11-25").

pub const fn supports_sse_transport(&self) -> bool

Whether this version uses HTTP+SSE transport (original spec).

Only V2024_11_05 uses the original HTTP+SSE transport. Later versions use Streamable HTTP.

pub const fn supports_streamable_http(&self) -> bool

Whether this version supports Streamable HTTP transport.

Added in 2025-03-26, replacing HTTP+SSE.

pub const fn supports_batching(&self) -> bool

Whether this version supports JSON-RPC batching.

Only available in 2025-03-26. Removed in 2025-06-18.

pub const fn requires_version_header(&self) -> bool

Whether the MCP-Protocol-Version header is required in HTTP requests.

Required from 2025-06-18 onwards.

pub const fn supports_audio_content(&self) -> bool

Whether this version supports audio content type.

Added in 2025-03-26.

pub const fn supports_tool_annotations(&self) -> bool

Whether this version supports tool annotations.

Tool annotations describe behavior like readOnly, destructive, idempotent. Added in 2025-03-26.

pub const fn supports_structured_tool_output(&self) -> bool

Whether this version supports structured tool output.

Allows tools to return structured data alongside text. Added in 2025-06-18.

pub const fn supports_resource_links(&self) -> bool

Whether this version supports resource links in tool results.

Allows tool results to reference resources. Added in 2025-06-18.

pub const fn supports_parallel_tools(&self) -> bool

Whether this version supports parallel tool calls.

Allows multiple tools to be called concurrently. Added in 2025-11-25.

pub const fn supports_oauth(&self) -> bool

Whether this version supports OAuth 2.1 authorization.

Added in 2025-03-26.

pub const fn supports_protected_resources(&self) -> bool

Whether this version supports protected resource metadata.

Enables discovery of OAuth authorization servers. Added in 2025-06-18.

pub const fn supports_elicitation(&self) -> bool

Whether this version supports elicitation.

Elicitation allows servers to request additional information from users. Added in 2025-06-18.

pub const fn supports_tasks(&self) -> bool

Whether this version supports tasks with async status tracking.

Tasks allow tracking long-running operations. Added in 2025-11-25.

pub const fn supports_agent_loops(&self) -> bool

Whether this version supports server-side agent loops.

Enables sophisticated multi-step reasoning on the server. Added in 2025-11-25.

pub const fn supports_sampling_tools(&self) -> bool

Whether this version supports tool calling in sampling requests.

Allows servers to include tool definitions in sampling. Added in 2025-11-25.

pub const fn supports_meta_field(&self) -> bool

Whether this version supports the _meta field in messages.

Provides metadata for messages. Added in 2025-06-18.

pub const fn supports_title_field(&self) -> bool

Whether this version supports the title field for display names.

Separate from name which is the programmatic identifier. Added in 2025-06-18.

pub const fn supports_completion_context(&self) -> bool

Whether this version supports the context field in completion requests.

Provides previously-resolved variable values. Added in 2025-06-18.

pub const fn supports_completions_capability(&self) -> bool

Whether this version supports the completions capability.

Explicitly indicates support for argument autocompletion. Added in 2025-03-26.

pub fn negotiate(requested: &str, supported: &[Self]) -> Option<Self>

Negotiate the best protocol version between requested and supported versions.

Returns the highest version that is:

1. Less than or equal to the requested version
2. In the supported versions list

Returns None if no compatible version exists.

Arguments

• requested - The version string requested by the client
• supported - List of versions supported by the server

Example

use mcpkit_core::protocol_version::ProtocolVersion;

// Server supports all versions, client requests latest
let negotiated = ProtocolVersion::negotiate(
    "2025-11-25",
    ProtocolVersion::ALL
);
assert_eq!(negotiated, Some(ProtocolVersion::V2025_11_25));

// Client requests older version
let negotiated = ProtocolVersion::negotiate(
    "2024-11-05",
    ProtocolVersion::ALL
);
assert_eq!(negotiated, Some(ProtocolVersion::V2024_11_05));

// Client requests unknown future version
let negotiated = ProtocolVersion::negotiate(
    "2026-01-01",
    ProtocolVersion::ALL
);
// Returns latest supported version
assert_eq!(negotiated, Some(ProtocolVersion::V2025_11_25));

pub const fn is_compatible_with(&self, client_version: Self) -> bool

Check if this version can communicate with another version.

Newer servers can communicate with older clients using backward compatibility.

Arguments

• client_version - The version the client supports

Example

use mcpkit_core::protocol_version::ProtocolVersion;

let server = ProtocolVersion::V2025_11_25;

// Server can talk to older clients
assert!(server.is_compatible_with(ProtocolVersion::V2024_11_05));

// Server can talk to same version
assert!(server.is_compatible_with(ProtocolVersion::V2025_11_25));

Trait Implementations

impl Clone for ProtocolVersion

fn clone(&self) -> ProtocolVersion

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ProtocolVersion

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ProtocolVersion

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for ProtocolVersion

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for ProtocolVersion

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl From<ProtocolVersion> for String

fn from(version: ProtocolVersion) -> Self

Converts to this type from the input type.

impl FromStr for ProtocolVersion

type Err = VersionParseError

The associated error which can be returned from parsing.

fn from_str(s: &str) -> Result<Self, Self::Err>

Parses a string s to return a value of this type.

impl Hash for ProtocolVersion

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for ProtocolVersion

fn cmp(&self, other: &ProtocolVersion) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for ProtocolVersion

fn eq(&self, other: &ProtocolVersion) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for ProtocolVersion

fn partial_cmp(&self, other: &ProtocolVersion) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Serialize for ProtocolVersion

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl TryFrom<&str> for ProtocolVersion

type Error = VersionParseError

The type returned in the event of a conversion error.

fn try_from(s: &str) -> Result<Self, Self::Error>

Performs the conversion.

impl TryFrom<String> for ProtocolVersion

type Error = VersionParseError

The type returned in the event of a conversion error.

fn try_from(s: String) -> Result<Self, Self::Error>

Performs the conversion.

impl Copy for ProtocolVersion

impl Eq for ProtocolVersion

impl StructuralPartialEq for ProtocolVersion