Struct ToolAnnotations 

pub struct ToolAnnotations {
    pub read_only_hint: Option<bool>,
    pub destructive_hint: Option<bool>,
    pub idempotent_hint: Option<bool>,
    pub open_world_hint: Option<bool>,
}

Behavioral hints for a tool, per the MCP 2025-03-26 spec’s tool annotations. Clients (Claude Desktop and others) use these to decide whether to warn or ask for confirmation before calling a tool — e.g. skip confirmation for a read-only tool, or warn before a destructive one.

Every field is a hint, not something this server enforces or verifies — nothing stops a handler registered with read_only_hint: Some(true) from actually writing to disk. A well-behaved server sets these accurately; a client is free to ignore them or ask for confirmation anyway.

Register with McpServer::tool_annotated. Build one with plain struct syntax — every field defaults to None (no hint given, the client’s own default applies):

use rust_web_server::mcp::ToolAnnotations;

let destructive = ToolAnnotations {
    destructive_hint: Some(true),
    read_only_hint: Some(false),
    ..Default::default()
};

Fields

read_only_hint: Option<bool>

The tool does not modify its environment.

destructive_hint: Option<bool>

The tool may perform destructive updates (only meaningful when read_only_hint is not Some(true)).

idempotent_hint: Option<bool>

Calling the tool repeatedly with the same arguments has no additional effect beyond the first call.

open_world_hint: Option<bool>

The tool may interact with an open-ended set of external entities (e.g. web search), as opposed to a fixed, closed set.

Trait Implementations

impl Clone for ToolAnnotations

fn clone(&self) -> ToolAnnotations

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for ToolAnnotations

impl Debug for ToolAnnotations

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

Formats the value using the given formatter.

impl Default for ToolAnnotations

fn default() -> ToolAnnotations

Returns the “default value” for a type.