The request "schema-builder" names no specific product, so the candidates are ranked on whether their sources show they build or manage schemas. DataHub 5 and CoreModels 6 are the clearest fits for schema mapping and definition, msgspec 9 and Cerberus 8 offer schema-based validation libraries, and Skeema.io 2 provides declarative schema management for MySQL and MariaDB.

1. 1

   DataHubdatahub.comfound in code, not yet checked

   Open-source data catalog whose actions include reading table column schemas and executing SQL against a warehouse 15.

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   +4 community tools built for it

   for agents: get_schema · datahub-skills · execute_sql

2. 2

   CoreModelscoremodels.iowebsite read, tools not yet checked

   Governed schema and meaning layer that imports, maps and exports schemas, with an MCP endpoint for agents 6.

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3. 3

   msgspecmsgspec.devverified and signed

   Serialization and validation library that uses Python type annotations as a zero-cost schema for JSON, MessagePack, YAML and TOML 9.

   WebsiteDocs

   for agents: schema · YAML · JSON

4. 4

   Cerberuspython-cerberus.orgverified and signed

   Lightweight Python data validation library where you define a validation schema as a dict and validate documents against it 8.

   WebsiteDocs

   for agents: schema · normalization · documents

5. 5

   Skeema.ioskeema.iowebsite read, tools not yet checked

   Declarative schema management for MySQL and MariaDB, tracking the desired schema state as CREATE statements in a repo 2.

   WebsiteDocs