Handle incompatible schemas (e.g. required of type []string) from older jsonschema drafts

[TeHeal]

It works normally when using the Python SDK, but the following issue occurs when using the Go SDK:
"Error calling the 'tools/list' interface: json: cannot unmarshal bool into Go struct field Tool.tools.inputSchema.schemaWithoutMethods.properties.schemaWithoutMethods.items.schemaWithoutMethods.properties.schemaWithoutMethods.required of type []string"

[findleyr]

Are you saying that required is a boolean in one of the schemas you're receiving from Python? Can you share transport logs (wrap your transport in an mcp.LoggingTransport)?

The "required" field must be of type []string, according to the JSON-schema spec:
https://json-schema.org/draft/2020-12/meta/validation

We need more information to understand what you're encountering.

[findleyr]

Here's a schema that produces exactly that error message for our Go jsonschema library:
https://www.jsonschemavalidator.net/s/A0m0C6nt
Note that it's valid for draft-03, but invalid for all subsequent drafts.

Furthermore, I've looked at the python SDK, and it is setting required to arrays in its test cases.

We really need more information to investigate this bug, such as a minimal repro or MCP logs. It sounds like you're using the Python client SDK to talk to some server, and it works, but they go SDK doesn't. That may be because the server is trying to use draft-03.

I don't know the relative distribution of jsonschema drafts, but I suspect that draft-03 is very rarely used.

[findleyr]

CC @jba

[jba]

Thanks for the json schema draft detective work, Rob. Indeed, I have never seen draft-03 used in the wild.

[jba]

One further question: if the server is sending schemas that have a $schema keyword referring to draft-03, then we could at least implement that draft and handle this case. (Not that we necessarily would do that, but we could.) However, if there is no $schema or a newer one, then I see no way to handle this while still having a compliant jsonschema implementation.

[findleyr]

Ok, I think we probably understand this, since we can assume the python SDK is handling the older draft, which probably means it has an explicit $schema keyword.

Retitling accordingly, and labeling this as both a 'bug' and a 'feature request' (it's arguably both).

[findleyr]

I think this should no longer be a problem with v0.8.0. @TeHeal could you confirm?

[TeHeal]

Yes, the issue has been resolved after upgrading to v0.8.0! The Go SDK can now properly handle the JSON schema compatibility issues we encountered before.
Thank you for your team's quick response and fix!

[findleyr]

Great! Thank you for confirming.