Struct Annotations 

pub struct Annotations {
    pub audience: Vec<Role>,
    pub priority: Option<f64>,
    pub last_modified: Option<String>,
    pub extensions: Extensions,
}

Annotations, added in 2025-03-26 (PR #185).

Modeled rather than dropped, because they are advisory metadata a client uses to decide how to present a result, and a tool that says it is read-only means something to the caller.

Not Eq, and neither is anything that holds one: priority is a floating-point number and neither f32 nor f64 is a valid Eq type, because of NaN. The cost is that a content block cannot be a HashMap key, which nothing needs — blocks live in a Vec inside a result.

priority is f64 rather than the f32 that would be conventional for a 0.0–1.0 quantity, because every revision’s generated Annotations spells it f64 and this crate’s whole job is to carry a peer’s value through unchanged. Narrowing on the way in and widening on the way out is not a round trip: 0.1_f32 is not 0.1_f64, and a bridge forwarding annotations would quietly change a number the sender chose.

Fields

audience: Vec<Role>

The audience this block is meant for.

priority: Option<f64>

How important this block is, 0.0–1.0.

f64 to match the wire exactly; see the type’s docs.

last_modified: Option<String>

The last time the resource was modified, ISO 8601.

extensions: Extensions

Unmodelled fields.

Implementations

impl Annotations

pub fn required_features(&self) -> FeatureSet

What these annotations need.

Annotations as a field need nothing: 2024-11-05 carries an untyped annotations on every content block, so a block with an audience and a priority lowers onto it and the value survives as JSON. That is why this is not Feature::ToolAnnotations, which gates the typed form added in 2025-03-26.

lastModified is different in kind, not degree. It exists only in the typed object, so an older revision cannot hold it at all — not as a field, not even untyped — and dropping it would lose information the sender put there. So it, and only it, requires 2025-06-18.

impl Annotations

pub const fn empty() -> Self

Annotations with nothing set.

Trait Implementations

impl Clone for Annotations

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 Annotations

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

Formats the value using the given formatter.

impl Default for Annotations

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq for Annotations

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Annotations