Trait ToolSource 

pub trait ToolSource: Send + Sync {
    // Required methods
    fn resolve_tools<'life0, 'async_trait>(
        &'life0 self,
    ) -> Pin<Box<dyn Future<Output = Result<Vec<ToolDefinition>>> + Send + 'async_trait>>
       where Self: 'async_trait,
             'life0: 'async_trait;
    fn source_name(&self) -> &str;
}

A dynamic source of tools, resolved fresh on every agent run instead of being frozen into the agent’s tool list at build time.

The motivating case is an MCP server: without this trait, wiring one into a crate::agent::Agent means calling mcp.tool_definitions().await once, up front, and handing the (now-frozen) result to crate::agent::AgentBuilder::tools — the agent never notices a server-side tool-catalog change (notifications/tools/list_changed) afterward. Registering a ToolSource via crate::agent::AgentBuilder::tool_source instead defers resolution to every crate::agent::SupportsAgentRun::run / crate::agent::SupportsAgentRun::run_with_options / crate::agent::SupportsAgentRun::run_stream call (see Agent::prepare_request), so a source that caches internally — invalidating that cache when the server signals a change — can serve an up-to-date catalog on every run without a live round trip each time.

See agent-framework-mcp’s McpStdioTool / McpStreamableHttpTool / McpWebsocketTool, which all implement this trait.

Required Methods

fn resolve_tools<'life0, 'async_trait>( &'life0 self, ) -> Pin<Box<dyn Future<Output = Result<Vec<ToolDefinition>>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Resolve this source’s current tools.

Called once per agent run. Implementations that connect to a remote server should connect lazily (on first call) and are encouraged to cache their result until something invalidates it, rather than performing a live round trip on every call.

An Err returned here propagates out of the whole run rather than being swallowed — this mirrors the upstream Python reference, whose Agent.run/run_stream do not catch a failure raised while connecting to an MCPTool at run time (_agents.py:855-865, 970-980: await self._async_exit_stack.enter_async_context(tool) is not wrapped in a try/except).

fn source_name(&self) -> &str

A short, human-readable name for this source, used in diagnostics (e.g. a tracing::warn! when one of its tools collides by name with a tool that already exists).

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors