Struct ProtocolVersion 

pub struct ProtocolVersion(/* private fields */);

Represents the MCP protocol version used for communication.

This ensures compatibility between clients and servers by specifying which version of the Model Context Protocol is being used.

Implementations

impl ProtocolVersion

pub const V_2026_07_28: Self

pub const V_2025_11_25: Self

pub const V_2025_06_18: Self

pub const V_2025_03_26: Self

pub const V_2024_11_05: Self

pub const LATEST: Self = Self::V_2026_07_28

The newest protocol version known to this SDK.

pub const STANDARD_HEADERS: Self = Self::V_2026_07_28

First protocol version that requires SEP-2243 standard HTTP headers.

pub const NO_INITIALIZE: Self = Self::V_2026_07_28

First protocol version that replaced the initialize handshake with per-request _meta (SEP-2567).

pub const LATEST_WITH_INITIALIZE: Self = Self::V_2025_11_25

The newest protocol version that still has an initialize handshake.

From Self::NO_INITIALIZE onward the lifecycle moved into per-request _meta, so there is no handshake left to answer. A server replying to initialize can therefore never name Self::LATEST once LATEST reaches that revision — it has to name this one instead.

Use this, not LATEST, whenever the subject is the handshake itself: the version a server can echo from initialize, or the version a test needs in order to exercise session-based behavior.

assert!(ProtocolVersion::LATEST_WITH_INITIALIZE.has_initialize());
assert!(!ProtocolVersion::LATEST.has_initialize());

pub const KNOWN_VERSIONS: &[Self]

All protocol versions known to this SDK, oldest first.

pub fn as_str(&self) -> &str

Returns the string representation of this protocol version.

pub fn has_initialize(&self) -> bool

Whether this revision negotiates its lifecycle over the initialize handshake.

false from Self::NO_INITIALIZE onward, where SEP-2567 moved the lifecycle into per-request _meta. Unknown versions are compared lexically, which orders correctly because every revision is dated YYYY-MM-DD.

assert!(ProtocolVersion::V_2025_11_25.has_initialize());
assert!(!ProtocolVersion::V_2026_07_28.has_initialize());

pub fn known_up_to(max: &Self) -> &'static [Self]

The known versions up to and including max, oldest first.

Servers that implement every revision up to some ceiling can return this from supported_protocol_versions instead of filtering Self::KNOWN_VERSIONS by hand. max itself need not be a known version; the result is empty when it predates all of them.

The result borrows from Self::KNOWN_VERSIONS, so call it directly in the method body — it needs no static and no LazyLock:

const MAX_SUPPORTED: ProtocolVersion = ProtocolVersion::V_2025_11_25;

fn supported_protocol_versions(&self) -> Cow<'static, [ProtocolVersion]> {
    Cow::Borrowed(ProtocolVersion::known_up_to(&MAX_SUPPORTED))
}

assert_eq!(
    ProtocolVersion::known_up_to(&ProtocolVersion::V_2025_06_18),
    &[
        ProtocolVersion::V_2024_11_05,
        ProtocolVersion::V_2025_03_26,
        ProtocolVersion::V_2025_06_18,
    ],
);

Trait Implementations

impl Clone for ProtocolVersion

fn clone(&self) -> Self

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 Eq for ProtocolVersion

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 JsonSchema for ProtocolVersion

Available on crate feature schemars only.

fn schema_name() -> Cow<'static, str>

The name of the generated JSON Schema.

fn schema_id() -> Cow<'static, str>

Returns a string that uniquely identifies the schema produced by this type.

fn json_schema(generator: &mut SchemaGenerator) -> Schema

Generates a JSON Schema for this type.

fn inline_schema() -> bool

Whether JSON Schemas generated for this type should be included directly in parent schemas, rather than being re-used where possible using the $ref keyword.

impl PartialEq for ProtocolVersion

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

Equality operator ==.

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

Inequality operator !=.

impl PartialOrd for ProtocolVersion

fn partial_cmp(&self, other: &Self) -> 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 StructuralPartialEq for ProtocolVersion