Struct Tool 

#[non_exhaustive]
pub struct Tool {
    pub name: String,
    pub namespaced_name: Option<String>,
    pub description: String,
    pub instructions: Option<String>,
    pub parameters: HashMap<String, Value>,
    pub overrides_built_in_tool: bool,
    pub skip_permission: bool,
    pub defer: Option<DeferMode>,
    /* private fields */
}

A tool that the client exposes to the Copilot agent.

Sent to the CLI as part of SessionConfig::tools / ResumeSessionConfig::tools at session creation/resume time. The Rust SDK hand-authors this struct (rather than using the schema-generated form) so it can carry runtime hints — overrides_built_in_tool, skip_permission — that don’t appear in the wire schema but are honored by the CLI.

A Tool may optionally carry a handler: an Arc<dyn ToolHandler> that implements the tool’s runtime behavior. When present, the SDK dispatches matching external_tool.requested broadcasts to it automatically. When absent (None), the tool is declaration-only — another connected client must service incoming invocations.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

name: String

Tool identifier (e.g., "bash", "grep", "str_replace_editor").

namespaced_name: Option<String>

Optional namespaced name for declarative filtering (e.g., "playwright/navigate" for MCP tools).

description: String

Description of what the tool does.

instructions: Option<String>

Optional instructions for how to use this tool effectively.

parameters: HashMap<String, Value>

JSON Schema for the tool’s input parameters.

overrides_built_in_tool: bool

When true, this tool replaces a built-in tool of the same name (e.g. supplying a custom grep that the agent uses in place of the CLI’s built-in implementation).

skip_permission: bool

When true, the CLI does not request permission before invoking this tool. Use with caution — the tool is responsible for any access control.

defer: Option<DeferMode>

Controls whether the tool may be deferred (loaded lazily via tool search) rather than always pre-loaded. When DeferMode::Auto, the tool can be deferred and surfaced through tool search. When DeferMode::Never, the tool is always pre-loaded. None lets the runtime decide.

Implementations

impl Tool

pub fn new(name: impl Into<String>) -> Self

Construct a new Tool with the given name and otherwise default values. The struct is #[non_exhaustive], so external callers cannot use struct-literal syntax — use this builder or Default::default plus mut-let.

Example

let tool = Tool::new("greet")
    .with_description("Say hello to a user")
    .with_parameters(json!({
        "type": "object",
        "properties": { "name": { "type": "string" } },
        "required": ["name"]
    }));

pub fn with_namespaced_name(self, namespaced_name: impl Into<String>) -> Self

Set the namespaced name for declarative filtering (e.g. "playwright/navigate" for MCP tools).

pub fn with_description(self, description: impl Into<String>) -> Self

Set the human-readable description of what the tool does.

pub fn with_instructions(self, instructions: impl Into<String>) -> Self

Set optional instructions for how to use this tool effectively.

pub fn with_parameters(self, parameters: Value) -> Self

Set the JSON Schema for the tool’s input parameters.

Accepts a JSON Schema as a serde_json::Value, typically built with serde_json::json!({...}) or returned by schema_for (available with the derive feature). Tool parameter schemas are always top-level JSON objects ({"type": "object", ...}).

Panics

Panics if parameters is not a JSON object. Use crate::tool::try_tool_parameters and assign to Tool::parameters directly when the schema comes from dynamic input and should produce a recoverable error instead.

pub fn with_overrides_built_in_tool(self, overrides: bool) -> Self

Mark this tool as overriding a built-in tool of the same name. E.g. supplying a custom grep that the agent uses in place of the CLI’s built-in implementation.

pub fn with_skip_permission(self, skip: bool) -> Self

When true, the CLI will not request permission before invoking this tool. Use with caution — the tool is responsible for any access control.

pub fn with_defer(self, defer: DeferMode) -> Self

Set the deferral mode controlling whether the tool may be loaded lazily via tool search (DeferMode::Auto) or always pre-loaded (DeferMode::Never).

pub fn with_handler(self, handler: Arc<dyn ToolHandler>) -> Self

Attach a runtime implementation. The SDK will dispatch matching external_tool.requested broadcasts to handler for this tool’s name. Without a handler the tool is declaration-only.

pub fn handler(&self) -> Option<&Arc<dyn ToolHandler>>

Returns the attached runtime handler, if any.

Read-only inspection — to install or replace a handler, use Tool::with_handler.

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 Default for Tool

fn default() -> Tool

Returns the “default value” for a type.

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.