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error TS2420: Class 'StreamableHTTPServerTransport' incorrectly implements interface 'Transport'. #1314
Description
I've updated to 1.25.1, and I get
../../node_modules/@modelcontextprotocol/sdk/dist/esm/server/streamableHttp.d.ts:58:22 - error TS2420: Class 'StreamableHTTPServerTransport' incorrectly implements interface 'Transport'.
Types of property 'onclose' are incompatible.
Type '(() => void) | undefined' is not assignable to type '() => void'.
Type 'undefined' is not assignable to type '() => void'.
58 export declare class StreamableHTTPServerTransport implements Transport {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Found 1 error.
I suspect this is due to "exactOptionalPropertyTypes": true in my tsconfig.json.
Activity
felixweinberger commentedon Dec 18, 2025
Thanks for reporting! We don't currently support
exactOptionalPropertyTypes- there are other type errors when enabled beyond this one.Workaround: Add
"skipLibCheck": trueto your tsconfig.json. This skips type checking of.d.tsfiles in node_modules (we use this ourselves).Probably won't get to this on the team in the short term but happy to review a PR.
fix: add `| undefined` to optional properties for exactOptionalProper…
fix(core): add | undefined to Transport optional callback types for e…
fix: support exactOptionalPropertyTypes in Transport interface
fix(core): add explicit | undefined to Transport interface optional p…
vultrarex21-dev commentedon Aug 24, 2026
Hi! I'd like to work on this issue.
I'll investigate the type errors caused by enabling
exactOptionalPropertyTypes, add the necessary fixes and regression tests, and submit a PR.Please let me know if there are any constraints or preferred approaches I should follow before I start.