Validate

Validate rejects a payload that doesn't conform to a schema or type, before it reaches an AI agent or an upstream MCP server or HTTP API. It's built on two primitives Zilla already uses to govern data everywhere in a config, not something specific to any one AI Gateway binding:

• Schema Registry defines where a schema lives: embedded in zilla.yaml, read from the local filesystem, or fetched from a remote schema registry.
• Schema Enforcement defines the type or schema a payload is checked against, from primitives like string and int32 to schema-backed formats like avro, json, and protobuf.

Validating Tool Call Arguments on mcp proxy

The mcp proxy binding's options.tools field validates tools/call request arguments directly against a primitive model, before the call is routed to an upstream:

options:
  tools: json

See the mcp proxy reference for the full set of supported primitive models.

Validating Tool Arguments and Responses on mcp-http

The mcp-http proxy binding validates both directions of a tool call: schemas.input checks the tools/call arguments before the upstream HTTP request is dispatched, and schemas.output checks the upstream HTTP response before it's surfaced as the tool result. Each is a converter binding a model to a catalog subject:

options:
  tools:
    create_pr:
      schemas:
        input:
          model: json
          catalog:
            my_catalog:
              - subject: create_pr_params
                version: latest
        output:
          model: json
          catalog:
            my_catalog:
              - subject: create_pr_result
                version: latest

A tools/call whose arguments don't conform to the resolved schema is rejected before the upstream request is made; an upstream response that doesn't conform to the output schema is rejected before it reaches the agent. mcp-http resources support the same schemas.output converter on resources/read. See the mcp-http reference for the full shape.

Validating HTTP Traffic Directly

Where a plain http binding fronts or proxies AI Gateway traffic outside of mcp/mcp-http, it accepts a model on request and response content, headers, path, and query parameters, using the same primitive model names:

options:
  requests:
    - path: /tools/call
      method: POST
      content:
        model: json
      responses:
        - status: 200
          content:
            model: json

See the http server and http client reference for the full set of options, including headers, path, and query validation.

Validating Against a Registered Schema

Wherever Zilla accepts a schema-backed model (avro, json, or protobuf), pairing it with a catalog validates against a schema resolved by subject, topic, or ID, rather than a fixed primitive type. Kafka Gateway's Validate uses exactly this pairing to validate Kafka message keys and values against a schema fetched from a registry, and mcp-http's schemas.input/schemas.output above use the identical model/catalog shape:

value:
  model: avro
  catalog:
    schema_registry:
      - strategy: topic

Next Steps

• Schema Registry covers each catalog type and when to use it.
• Schema Enforcement covers each model type, from primitives to schema-backed formats.
• Transform covers transforming a payload's representation once it's validated.