Protocol version diff
MCP 2025-11-25 vs 2026 tool schema changes
Understand JSON Schema 2020-12 support, root rules, and output schema changes in the MCP 2026 release candidate.
The 2026 release candidate expands full JSON Schema 2020-12 support. Input schemas retain an object root, while output schemas become unrestricted—a meaningful difference for scalar and array tool results.
Read the schema and its provider wrapper as one contract. APITC distinguishes target requirements from portable JSON Schema, applies mechanical repairs only when intent is recoverable, and identifies transformations that can change meaning.
Diagnostic procedure
Repair the schema, then recompile.
- 01
Pin the protocol target
Validate against the client and server revision you actually deploy.
- 02
Review output roots
Scalar or array output contracts need a compatibility wrapper for 2025-era consumers.
- 03
Preserve schema dialect
Use an explicit $schema when consuming 2020-12 vocabulary across toolchains.
2025-11-25 outputSchema: object-root structured output
2026 RC outputSchema: unrestricted JSON Schema 2020-12 output
$.inputSchemaClose this objectOpenAI strict requires additionalProperties: false on every object.
$.inputSchemaRequired array is incompleteStrict mode requires every property in required. APITC will make limit nullable.
No account · no upload · no endpoint calledOpen the full tool schema compiler and operating notes →
FAQ
Before you ship
Does APITC upload my schema?
No. Parsing, diagnostics, and compilation run in your browser tab.
Is the compiled result guaranteed to preserve meaning?
Safe repairs are deterministic. When MCP cannot express a source constraint, APITC labels the transform as lossy instead of hiding it.
Protocol behavior checked against the MCP 2026 release candidate. Recheck your pinned provider/API version before production deployment.