InitializeRequest doesn't accept non-empty Elicitation, violating 2025-11-25 spec

Bug description
An initialize request with "capabilities":{"elicitation":{"form":{}}} causes this error:

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "form" (class io.modelcontextprotocol.spec.McpSchema$ClientCapabilities$Elicitation), not marked as ignorable (0 known properties: ])
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 72] (through reference chain: io.modelcontextprotocol.spec.McpSchema$InitializeRequest["capabilities"]->io.modelcontextprotocol.spec.McpSchema$ClientCapabilities["elicitation"]->io.modelcontextprotocol.spec.McpSchema$ClientCapabilities$Elicitation["form"])

This violates the 2025-11-25 spec.

Environment
N/A

Steps to reproduce
run test shown below

Expected behavior
test succeeds

Minimal Complete Reproducible example

@Test
void testParseInitializeRequest() throws IOException {
	String serialized = """
			{"protocolVersion":"2024-11-05","capabilities":{"elicitation":{"form":{}}},"clientInfo":{"name":"test-client","version":"1.0.0"},"_meta":{"metaKey":"metaValue"}}
			""";

	McpSchema.InitializeRequest deserialized = JSON_MAPPER.readValue(serialized, McpSchema.InitializeRequest.class);

	McpSchema.ClientCapabilities capabilities = McpSchema.ClientCapabilities.builder()
			.elicitation()
			.build();
	McpSchema.Implementation clientInfo = new McpSchema.Implementation("test-client", "1.0.0");
	Map<String, Object> meta = Map.of("metaKey", "metaValue");
	McpSchema.InitializeRequest expected = new McpSchema.InitializeRequest(ProtocolVersions.MCP_2024_11_05,
			capabilities, clientInfo, meta);
	assertThat(deserialized).isEqualTo(expected);
}

fix modelcontextprotocol#724

Hello,
I don't know if it may help to have a scenario, but I experienced this error after trying in VSCode the McpStatelessAsyncServer through HTTP protocol.
Cheers

Same for me, VSCode appears to be using the new spec already, but servers using this SDK can't handle it.

In my case I was trying to include the SonarQube MCP server.

I know that maybe the proper fix is to implement the newer spec, but in the meantime this problem is blocking. Any chance to get the fix upstream?

@overheadhunter

@overheadhunter SQ MCP Server developer here - I'll provide a fix for our next version, the JSON mapper should not fail on unknown properties.

fix: Support form and url fields in Elicitation capability per 2025-1…

I've opened a PR to address this: #731

I've opened a PR to address this: #731

do you want to add your changes to the existing PR? there has been some activity on it already.

I had missed your original PR. I'm not sure if I can merge mine to your PR, I will let maintainers decide

@overheadhunter

Can you get this fixed :) as its a huge blocker of our daily workflow. Thank you for the great work tool tho!

@overheadhunter @nquinquenel

@rhtnr

I'm not sure if I can merge mine to your PR, I will let maintainers decide

@rhtnr You can create a PR against this branch: https://github.com/overheadhunter/mcp-java-sdk/tree/fix-724. The combined changes should then show up on PR #725

fix: Support form and url fields in Elicitation capability per 2025-1…

@overheadhunter

@overheadhunter
I've opened a PR against your branch with additional field modeling for form and url: overheadhunter#1

This combines your @JsonIgnoreProperties approach with explicit field support, giving us both future-proofing and proper parsing/serialization of the spec fields.

I resolved this issue by using a servlet filter. (on spring-ai)

dependency: spring-ai-starter-mcp-server-webmvc:1.1.2

spring-projects/spring-ai#5133 (comment)

fix: Support form and url fields in Elicitation capability per 2025-1…

fix(mcp-server): ignore unknown properties during deserialisation

~~In which version this fix will be released?~~
nvm, github does not show the minor release with the fix in the main page of the project

fix(mcp-server): ignore unknown properties during deserialisation

@JsonIgnoreProperties

Add @JsonIgnoreProperties(ignoreUnknown = true) to capability sub-rec…

link #115926 Upgrade MCP SDK fork to upstream v0.18.2 for streamable …

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`InitializeRequest` doesn't accept non-empty Elicitation, violating 2025-11-25 spec #724

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InitializeRequest doesn't accept non-empty Elicitation, violating 2025-11-25 spec #724

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fansanelli commented on Dec 15, 2025

overheadhunter commented on Dec 15, 2025

fansanelli commented on Dec 17, 2025

nquinquenel commented on Dec 17, 2025

rhtnr commented on Dec 20, 2025

overheadhunter commented on Dec 20, 2025

rhtnr commented on Dec 20, 2025

khobiziilyes commented on Dec 30, 2025

overheadhunter commented on Jan 7, 2026

rhtnr commented on Jan 8, 2026

devxb commented on Jan 8, 2026

afucher commented on Jan 14, 2026

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`InitializeRequest` doesn't accept non-empty Elicitation, violating 2025-11-25 spec #724