Struct Tool 

pub struct Tool {
    pub annotations: Option<ToolAnnotations>,
    pub description: Option<String>,
    pub icons: Vec<Icon>,
    pub input_schema: ToolInputSchema,
    pub meta: Option<MetaObject>,
    pub name: String,
    pub output_schema: Option<ToolOutputSchema>,
    pub title: Option<String>,
}

Latest MCP Protocol 2026_07_28 Definition for a tool the client can call.

JSON schema

{
 "description": "Definition for a tool the client can call.",
 "type": "object",
 "required": [
   "inputSchema",
   "name"
 ],
 "properties": {
   "_meta": {
     "$ref": "#/$defs/MetaObject"
   },
   "annotations": {
     "description": "Optional additional tool information.\n\nDisplay name precedence order is: title, annotations.title, then name.",
     "$ref": "#/$defs/ToolAnnotations"
   },
   "description": {
     "description": "A human-readable description of the tool.\n\nThis can be used by clients to improve the LLM's understanding of available tools. It can be thought of like a \"hint\" to the model.",
     "type": "string"
   },
   "icons": {
     "description": "Optional set of sized icons that the client can display in a user interface.\n\nClients that support rendering icons MUST support at least the following MIME types:\n- image/png - PNG images (safe, universal compatibility)\n- image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)\n\nClients that support rendering icons SHOULD also support:\n- image/svg+xml - SVG images (scalable but requires security precautions)\n- image/webp - WebP images (modern, efficient format)",
     "type": "array",
     "items": {
       "$ref": "#/$defs/Icon"
     }
   },
   "inputSchema": {
     "description": "A JSON Schema object defining the expected parameters for the tool.\n\nTool arguments are always JSON objects, so type: \"object\" is required at the root.\nBeyond that, any JSON Schema 2020-12 keyword may appear alongside type — including\ncomposition keywords (oneOf, anyOf, allOf, not), conditional keywords\n(if/then/else), reference keywords ($ref, $defs, $anchor), and any other\nstandard validation or annotation keywords.\n\nProperty schemas may carry an x-mcp-header annotation to mirror the\nargument value into an HTTP header on the Streamable HTTP transport. See\nthe Streamable HTTP transport specification for the validity and\nextraction rules.\n\nDefaults to JSON Schema 2020-12 when no explicit $schema is provided.",
     "type": "object",
     "required": [
       "type"
     ],
     "properties": {
       "$schema": {
         "type": "string"
       },
       "type": {
         "type": "string",
         "const": "object"
       }
     },
     "additionalProperties": {}
   },
   "name": {
     "description": "Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).",
     "type": "string"
   },
   "outputSchema": {
     "description": "An optional JSON Schema object defining the structure of the tool's output returned in\nthe structuredContent field of a {@link CallToolResult}. This can be any valid JSON Schema 2020-12.\n\nDefaults to JSON Schema 2020-12 when no explicit $schema is provided.",
     "type": "object",
     "properties": {
       "$schema": {
         "type": "string"
       }
     },
     "additionalProperties": {}
   },
   "title": {
     "description": "Intended for UI and end-user contexts — optimized to be human-readable and easily understood,\neven by those unfamiliar with domain-specific terminology.\n\nIf not provided, the name should be used for display (except for {@link Tool},\nwhere annotations.title should be given precedence over using name,\nif present).",
     "type": "string"
   }
 }
}

Fields

annotations: Option<ToolAnnotations>

Optional additional tool information. Display name precedence order is: title, annotations.title, then name.

description: Option<String>

A human-readable description of the tool. This can be used by clients to improve the LLM’s understanding of available tools. It can be thought of like a “hint” to the model.

icons: Vec<Icon>

Optional set of sized icons that the client can display in a user interface. Clients that support rendering icons MUST support at least the following MIME types: - image/png - PNG images (safe, universal compatibility) - image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility) Clients that support rendering icons SHOULD also support: - image/svg+xml - SVG images (scalable but requires security precautions) - image/webp - WebP images (modern, efficient format)

input_schema: ToolInputSchema

meta: Option<MetaObject>

name: String

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).

output_schema: Option<ToolOutputSchema>

title: Option<String>

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology. If not provided, the name should be used for display (except for {@link Tool}, where annotations.title should be given precedence over using name, if present).

Trait Implementations

impl Clone for Tool

fn clone(&self) -> Tool

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Tool

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Tool

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for Tool

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

where __S: Serializer,

Serialize this value into the given Serde serializer.