feat(mcp): support sampling in a scoped way by alexhancock · Pull Request #5367 · block/goose

alexhancock · 2025-10-24T21:39:33Z

Implements basic support for MCP Sampling

MCP servers can now request sampling and it will be handled by goose to route a sampling message to the provider for completion
Works for desktop and CLI
Does not yet implement human in the loop approval of these, which is a SHOULD for clients in the MCP spec, but added significant overhead to the initial implementation so the idea is to get a scoped and working implementation out and then iterate
Sampling is supposed to be text, image, or audio. This does not handle audio, because interestingly goose does not handle audio message content. Can be a followup when we support it generally.

Demos of it working in CLI and Desktop with the everything server the prompt

Use the sampleLLM tool in the everything extension to have the mcp server request sampling from the model. Have the mcp server ask the model for a quote from the great gatsby

jamadeo

nice!

jamadeo · 2025-10-25T01:33:00Z

crates/goose/src/agents/mcp_client.rs

-    ClientHandler, Peer, RoleClient, ServiceError, ServiceExt,
+    ClientHandler, ErrorData as McpError, ErrorData, Peer, RoleClient, ServiceError, ServiceExt,
 };
+use schemars::_private::NoSerialize;


suspicious-looking import!

It was needed for e.maybe_to_value() but no longer using that, so it's gone!

jamadeo · 2025-10-25T01:33:51Z

crates/goose/src/agents/extension_manager_extension.rs


        let result = extension_manager
-            .add_extension(config)
+            .add_extension(config, None)


probably fine for now, but I suppose we will want to allow this to work too

In theory I fixed this in the most recent commit, which changes the approach of how the extension manager has a reference to a provider. Didn't text explicitly for sampling through extension_manager managed extensions, but I think it may work now. I'll add a note to follow up on it.

DOsinga

This generally looks good and would allow us to ship something. I'm a little concerned on how we handle providers. within the context of mcp, I don't think they should be optional - we can't have an MCP call without a provider, right?

the other is that we now set a provider on the extension_manager. in some scenarios we might not have it yet, maybe that's why it is optional? but I don't think we can be sure we're using the right provider if the user switches models, providers etc.

we should use the provider of the agent I think.

DOsinga · 2025-10-26T13:27:22Z

crates/goose/src/agents/mcp_client.rs

+                ErrorData::new(
+                    ErrorCode::INTERNAL_ERROR,
+                    "Unexpected error while completing the prompt",
+                    e.maybe_to_value(),


why maybe_to_value()? I think ti would return None here, we should probably return the relevant string though

alexhancock · 2025-10-28T21:16:10Z

@jamadeo @DOsinga Updated it to always uses the agent's current provider via a shared reference. Verified by the llm_request logs that it uses different models for sampling after switching providers.

DOsinga

how do we test this?

crates/goose/src/agents/types.rs

crates/goose/src/agents/mcp_client.rs

DOsinga · 2025-10-29T13:21:40Z

crates/goose/src/agents/mcp_client.rs

+            })?;
+
+        // convert back to MCP messages
+        let response_content = if let Some(content) = response.content.first() {


only first?

alexhancock · 2025-10-29T21:13:45Z

Draft of a couple different approaches to integration testing for sampling #5456

Wanted to make a separate PR to get feedback on which one seems most valuable

@jamadeo @DOsinga

Signed-off-by: fbalicchia <fbalicchia@gmail.com>

Signed-off-by: Blair Allan <Blairallan@icloud.com>

alexhancock requested review from DOsinga and jamadeo October 24, 2025 21:39

jamadeo approved these changes Oct 25, 2025

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DOsinga reviewed Oct 26, 2025

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alexhancock force-pushed the alexhancock/mcp-sampling branch 8 times, most recently from 30943fd to c84f539 Compare October 28, 2025 21:11

alexhancock force-pushed the alexhancock/mcp-sampling branch from c84f539 to 93afbd6 Compare October 29, 2025 13:14

DOsinga approved these changes Oct 29, 2025

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alexhancock force-pushed the alexhancock/mcp-sampling branch 5 times, most recently from fa587e7 to 1680290 Compare October 29, 2025 18:49

feat(mcp): support sampling in a scoped way

3e2bc35

alexhancock force-pushed the alexhancock/mcp-sampling branch from 1680290 to 3e2bc35 Compare October 29, 2025 20:43

alexhancock merged commit 06b7a63 into main Oct 29, 2025
14 checks passed

alexhancock deleted the alexhancock/mcp-sampling branch October 29, 2025 21:06

alexhancock mentioned this pull request Oct 29, 2025

chore(tests/mcp): testing for MCP sampling #5456

Merged

github-actions bot mentioned this pull request Nov 5, 2025

chore(release): release version 1.13.0 (minor) #5582

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fbalicchia pushed a commit to fbalicchia/goose that referenced this pull request Nov 7, 2025

feat(mcp): support sampling in a scoped way (block#5367)

0e9225e

Signed-off-by: fbalicchia <fbalicchia@gmail.com>

BlairAllan pushed a commit to BlairAllan/goose that referenced this pull request Nov 29, 2025

feat(mcp): support sampling in a scoped way (block#5367)

a2490fa

Signed-off-by: Blair Allan <Blairallan@icloud.com>

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alexhancock commented Oct 28, 2025 •

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