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InitializeRequest doesn't accept non-empty Elicitation, violating 2025-11-25 spec #724
Description
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);
}
Activity
fix modelcontextprotocol#724
fansanelli commentedon Dec 15, 2025
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
overheadhunter commentedon Dec 15, 2025
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.
fansanelli commentedon Dec 17, 2025
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?
nquinquenel commentedon Dec 17, 2025
@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…
rhtnr commentedon Dec 20, 2025
I've opened a PR to address this: #731
overheadhunter commentedon Dec 20, 2025
do you want to add your changes to the existing PR? there has been some activity on it already.
rhtnr commentedon Dec 20, 2025
I had missed your original PR. I'm not sure if I can merge mine to your PR, I will let maintainers decide
khobiziilyes commentedon Dec 30, 2025
Can you get this fixed :) as its a huge blocker of our daily workflow. Thank you for the great work tool tho!
@overheadhunter @nquinquenel
overheadhunter commentedon Jan 7, 2026
@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…
rhtnr commentedon Jan 8, 2026
@overheadhunter
I've opened a PR against your branch with additional field modeling for
formandurl: overheadhunter#1This combines your
@JsonIgnorePropertiesapproach with explicit field support, giving us both future-proofing and proper parsing/serialization of the spec fields.devxb commentedon Jan 8, 2026
I resolved this issue by using a servlet filter. (on spring-ai)
spring-projects/spring-ai#5133 (comment)
fix: Support form and url fields in Elicitation capability per 2025-1…
fix: Support form and url fields in Elicitation capability per 2025-1…
fix: Support form and url fields in Elicitation capability per 2025-1…
fix(mcp-server): ignore unknown properties during deserialisation
afucher commentedon Jan 14, 2026
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
Add @JsonIgnoreProperties(ignoreUnknown = true) to capability sub-rec…
link #115926 Upgrade MCP SDK fork to upstream v0.18.2 for streamable …