`json_validate`

Validate JSON from context against a JSON Schema.

Parameters

source_keystringrequired: Context key containing either a JSON string, or a value already decoded as JSON
schemaobject*: A JSON Schema object to validate the data against
schema_keystring*: Context key containing a JSON Schema object or JSON Schema string

*Provide exactly one of schema or schema_key.

If the value is a string, json_validate first parses it as JSON, then validates the result.
If the value is already a JSON object/array/etc., it is validated directly.

Context Output

validation_success — boolean indicating whether validation passed
validation_errors — array of validation error strings (empty on success)

The node returns a structured error when validation fails. Downstream steps are skipped unless a dedicated on_error handler runs successfully and resolves the failure. After retries are exhausted, the final validation result is buffered for the source phase barrier and the handler receives its source-exact copy in _error_output. Normal shared keys still follow declaration-order collision precedence if a parallel step publishes the same names.

Example

local flow = Flow.new("json_validate_example")

flow:step("validate", nodes.json_validate({
    source_key = "payload_json",
    schema = {
        type = "object",
        required = { "id", "name" },
        properties = {
            id = { type = "string" },
            name = { type = "string" },
            age = { type = "integer", minimum = 0 }
        }
    }
}))

flow:step("ok", nodes.log({
    message = "Payload JSON passed validation."
})):depends_on("validate")

return flow

Validate with a schema loaded from a file

local flow = Flow.new("json_validate_from_file")

flow:step("read_schema", nodes.read_file({
    path = "schemas/payload.schema.json",
    output_key = "schema"
}))

flow:step("validate", nodes.json_validate({
    source_key = "payload_json",
    schema_key = "schema_content"
})):depends_on("read_schema")

return flow