Enum Capability 

pub enum Capability {
    Experimental,
    Extensions,
    Roots,
    RootsListChanged,
    Sampling,
    SamplingContext,
    SamplingTools,
    Elicitation,
    ElicitationForm,
    ElicitationUrl,
    Logging,
    Prompts,
    PromptsListChanged,
    Resources,
    ResourcesListChanged,
    ResourcesSubscribe,
    Tools,
    ToolsListChanged,
    Completions,
    Tasks,
    TasksCancel,
    TasksList,
    TasksRequests,
    TasksRequestsElicitation,
    TasksRequestsElicitationCreate,
    TasksRequestsSampling,
    TasksRequestsSamplingCreateMessage,
    TasksRequestsTools,
    TasksRequestsToolsCall,
}

A capability name as the specification spells it.

Fieldless, and one variant per leaf name in the capability trees. The container names (roots, tasks, …) are variants too: a peer that advertises roots has advertised that it has roots, and a feature gate on “the peer has roots at all” is a real question that FeatureProfile has to answer.

Variants

Experimental

Client and server experimental bags. Present in every revision.

Extensions

extensions, new in 2026-07-28 on both sides.

Roots

Client roots. Deprecated in 2026-07-28 but still defined.

RootsListChanged

Client roots.listChanged, removed in 2026-07-28 along with the notifications/roots/list_changed method.

Sampling

Client sampling. Deprecated in 2026-07-28 but still defined.

SamplingContext

Client sampling.context, added 2025-11-25.

SamplingTools

Client sampling.tools, added 2025-11-25 (SEP-1577).

Elicitation

Client elicitation, added 2025-06-18.

ElicitationForm

Client elicitation.form, added 2025-11-25 (SEP-1330).

ElicitationUrl

Client elicitation.url, added 2025-11-25 (SEP-1036).

Logging

Server logging. Deprecated in 2026-07-28; logging/setLevel is removed, log level moves to _meta.

Prompts

Server prompts, every revision.

PromptsListChanged

Server prompts.listChanged, every revision.

Resources

Server resources, every revision.

ResourcesListChanged

Server resources.listChanged, every revision.

ResourcesSubscribe

Server resources.subscribe. The methods behind it are replaced in 2026-07-28; the capability is not.

Tools

Server tools, every revision.

ToolsListChanged

Server tools.listChanged, every revision.

Completions

Server completions, added 2025-03-26.

Tasks

tasks, added 2025-11-25 (SEP-1686) on both sides and removed from both in 2026-07-28, where it moves to the io.modelcontextprotocol/tasks extension (SEP-2663).

TasksCancel

Client and server tasks.cancel, 2025-11-25 only.

TasksList

Client and server tasks.list, 2025-11-25 only. The method was removed in 2026-07-28 along with the capability.

TasksRequests

Client and server tasks.requests, 2025-11-25 only.

TasksRequestsElicitation

Client tasks.requests.elicitation, 2025-11-25 only.

TasksRequestsElicitationCreate

Client tasks.requests.elicitation.create, 2025-11-25 only.

TasksRequestsSampling

Client tasks.requests.sampling, 2025-11-25 only.

TasksRequestsSamplingCreateMessage

Client tasks.requests.sampling.createMessage, 2025-11-25 only.

TasksRequestsTools

Server tasks.requests.tools, 2025-11-25 only.

TasksRequestsToolsCall

Server tasks.requests.tools.call, 2025-11-25 only.

Implementations

impl Capability

pub const ALL: [Self; 29]

Every capability, in declaration order.

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

The name the specification uses, dot-separated.

pub const fn side(self) -> Side

Which side declares it.

pub fn bit(self) -> u128

The bit this capability occupies in a CapabilitySet.

The index is the position in Capability::ALL, found by name rather than written by hand, so adding a variant cannot leave a stale hand-assigned bit behind. Asserted to be a distinct in-range power of two by every_capability_fits_in_the_bitset.

Not const: the indexing_slicing lint is denied workspace-wide, and slice::get — the non-panicking form it demands — is not a const-callable function on 1.98. The two cannot both be satisfied, and an unchecked index in a const fn is not worth suppressing the lint for: nothing here is evaluated at compile time.

pub fn defined_in(self, version: ProtocolVersion) -> bool

Whether the given revision defines this capability at all.

Not the same question as whether a particular peer advertises it: a revision either has the name in its schema or it does not, and a peer on that revision either sends it or does not.

Trait Implementations

impl Clone for Capability

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Capability

impl Debug for Capability

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

Formats the value using the given formatter.

impl Display for Capability

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

Formats the value using the given formatter.

impl Eq for Capability

impl Hash for Capability

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 Capability

fn cmp(&self, other: &Self) -> 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.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for Capability

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

Equality operator ==.

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

Inequality operator !=.

impl PartialOrd for Capability

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 StructuralPartialEq for Capability