MCP JSON Schema

Generates JSON Schema for MCP servers from a Jackson 3 annotated Java class.

This library targets the Model Context Protocol (MCP) JSON Schema, which is a subset of the general JSON Schema specification. For details on the MCP JSON Schema subset and primitive types, see the MCP PrimitiveSchemaDefinition.

See Generate MCP Tool Schemas Directly From Java Code

Usage

Define Your MCP Tool Parameters Type

Create a Jackson‑annotated record or Java class that represents the tool's input parameters. Use @JsonProperty(required=true, defaultValue=...) and @JsonPropertyDescription to enrich the schema. Use Jakarta validations like @Max,@Min, @Positive, @PositiveOrZero, @Negative, @NegativeOrZero on numbers, or @Size, @NotBlank on strings.

Here is an example:

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyDescription;
import tools.jackson.databind.PropertyNamingStrategies;
import tools.jackson.databind.annotation.JsonNaming;

@JsonNaming(PropertyNamingStrategies.KebabCaseStrategy.class)
public record SampleParameters(
    @JsonPropertyDescription("Type of database table dependant objects.")
    @JsonProperty(defaultValue = "NONE", required = true)
    DependantObjectType dependantObjectType,

    @JsonPropertyDescription("Table name.")
    String tableName) {

  public enum DependantObjectType { NONE, COLUMNS, INDEXES, FOREIGN_KEYS, TRIGGERS }
}

Generate the MCP inputSchema for Tool Registration

When registering your MCP tool, use McpJsonSchemaUtility.inputSchema(...) to generate the inputSchema JSON for the parameters type.

import us.fatehi.mcp_json_schema.McpJsonSchemaUtility;

// Provide this value as the tool's input_schema in your MCP server implementation
String inputSchemaJson = McpJsonSchemaUtility.inputSchema(SampleParameters.class);

You can also obtain the schema as a Jackson JsonNode if you prefer to embed or modify it programmatically:

var schemaNode = McpJsonSchemaUtility.generateJsonSchema(SampleParameters.class);

Instantiate Arguments for Execution

When the tool is invoked by a client, you'll receive an arguments JSON string. Convert it into your parameters type using instantiateArguments(...).

import tools.jackson.databind.JsonNode;
import us.fatehi.mcp_json_schema.DeserializationUtility;

String arguments = """
{
  "dependant-object-type": "COLUMNS",
  "table-name": "customers"
}
""";

SampleParameters argsObject = 
  DeserializationUtility.instantiateArguments(arguments, SampleParameters.class);