JSON Schema 2020-12 and the Contract for Context | Ola Hungerford | MCP Release Party - Seattle
This talk details the critical evolution of the Model Context Protocol (MCP), emphasizing that the schema acts as the 'contract for context' between tools and LLMs. The major update is the adoption of JSON Schema 2020-12 for tool definitions, replacing previous limited subsets. This upgrade significantly enhances expressiveness in both input and output schemas, allowing developers to use advanced keywords (like `allOf` and conditional constraints) and enabling better pre-LLM validation.
Key takeaways
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Schema as Contract
In MCP, the schema defines the contract for context—how a tool specifies what data it accepts and returns. This is crucial for reliable LLM interaction.
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Adoption of JSON Schema 2020-12
2:34
MCP now conforms to JSON Schema 2020-12, aligning with the default dialect used by OpenAPI 3.1. This was achieved via SEP 2106 and expands support beyond previous limited subsets.
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Enhanced Input/Output Schemas
3:55
Input schemas gain full JSON Schema 2020-12 support, allowing for complex conditional keywords (e.g., `allOf`). Output schemas no longer face the same restrictive limitations as before.