Adding streaming tool calls for progress updates from long-running tools

[santu8597]

Discussion: Progress updates from long-running tools

Hi everyone,

While going through the MoFA codebase and trying to understand how tool execution works, I noticed that tools currently behave like atomic operations — they run and then return a single result at the end.

From what I saw, the ToolExecutor trait looks like this:

async fn execute(&self, arguments: serde_json::Value) -> PluginResult<serde_json::Value>;

So the agent calls the tool, waits for it to finish, and then uses the returned value.

For most tools this seems totally fine, but I was wondering about long-running tools like web scraping, shell commands, or heavy file processing. In those cases the agent just waits until the tool finishes, and there’s no way for the tool to emit intermediate messages like:

[WebScraper] Downloading page...
[WebScraper] Parsing HTML...
[WebScraper] Extracting links...

I tried tracing the execution path a bit and it seems like tools don’t currently receive any kind of context or event emitter — they only get the JSON arguments. Because of that, there isn’t really a way for them to send progress updates back to the runtime.

My initial thought was that something like a small execution context might make this possible, for example:

async fn execute(
    &self,
    ctx: ToolContext,
    arguments: serde_json::Value
) -> PluginResult<serde_json::Value>;

where the context could optionally expose something like a progress sender or event emitter.

That said, it also looks like this would touch quite a few parts of the system (the tool trait, plugin runtimes, agent loop, event system, etc.), so it might not be something the architecture is meant to support.

So I mainly wanted to ask:

Is the current “single result” tool model an intentional design choice?
Or is emitting progress updates from tools something that could make sense for MoFA in the future?

Thanks!

[santu8597]

@yangrudan @LuigiGonnella @doroteaMonaco it would be very helpful, if you give your opinion on this.