Advanced Hasura GraphQL MCP Server

Instructions

Implementation Reference

• src/index.ts:247-280 (registration)

  Registers the MCP tool 'list_root_fields' with description, input schema, and handler function.

  server.tool(
    "list_root_fields",
    "Lists the available top-level query, mutation, or subscription fields...",
    {
      fieldType: z.enum(["QUERY", "MUTATION", "SUBSCRIPTION"]).optional().describe("Optional. Filter by 'QUERY'...")
    },
    async ({ fieldType }) => {
      console.log(`[INFO] Executing tool 'list_root_fields', filtering by: ${fieldType || 'ALL'}`);
      try {
        const schema = await getIntrospectionSchema();
        let fields: IntrospectionField[] = [];
        if ((!fieldType || fieldType === "QUERY") && schema.queryType) {
            const queryRoot = schema.types.find(t => t.name === schema.queryType?.name) as IntrospectionObjectType | undefined;
            fields = fields.concat(queryRoot?.fields || []);
        }
        if ((!fieldType || fieldType === "MUTATION") && schema.mutationType) {
            const mutationRoot = schema.types.find(t => t.name === schema.mutationType?.name) as IntrospectionObjectType | undefined;
            fields = fields.concat(mutationRoot?.fields || []);
        }
        if ((!fieldType || fieldType === "SUBSCRIPTION") && schema.subscriptionType) {
            const subscriptionRoot = schema.types.find(t => t.name === schema.subscriptionType?.name) as IntrospectionObjectType | undefined;
            fields = fields.concat(subscriptionRoot?.fields || []);
        }
        const fieldInfo = fields.map(f => ({
            name: f.name,
            description: f.description || "No description.",
        })).sort((a, b) => a.name.localeCompare(b.name));
        return { content: [{ type: "text", text: JSON.stringify(fieldInfo, null, 2) }] };
      } catch (error: any) {
        console.error(`[ERROR] Tool 'list_root_fields' failed: ${error.message}`);
        throw error;
      }
    }
  );

• src/index.ts:253-279 (handler)

  Executes the tool by fetching the GraphQL introspection schema, collecting fields from query/mutation/subscription root types based on optional fieldType filter, formats name and description, sorts, and returns as JSON.

  async ({ fieldType }) => {
    console.log(`[INFO] Executing tool 'list_root_fields', filtering by: ${fieldType || 'ALL'}`);
    try {
      const schema = await getIntrospectionSchema();
      let fields: IntrospectionField[] = [];
      if ((!fieldType || fieldType === "QUERY") && schema.queryType) {
          const queryRoot = schema.types.find(t => t.name === schema.queryType?.name) as IntrospectionObjectType | undefined;
          fields = fields.concat(queryRoot?.fields || []);
      }
      if ((!fieldType || fieldType === "MUTATION") && schema.mutationType) {
          const mutationRoot = schema.types.find(t => t.name === schema.mutationType?.name) as IntrospectionObjectType | undefined;
          fields = fields.concat(mutationRoot?.fields || []);
      }
      if ((!fieldType || fieldType === "SUBSCRIPTION") && schema.subscriptionType) {
          const subscriptionRoot = schema.types.find(t => t.name === schema.subscriptionType?.name) as IntrospectionObjectType | undefined;
          fields = fields.concat(subscriptionRoot?.fields || []);
      }
      const fieldInfo = fields.map(f => ({
          name: f.name,
          description: f.description || "No description.",
      })).sort((a, b) => a.name.localeCompare(b.name));
      return { content: [{ type: "text", text: JSON.stringify(fieldInfo, null, 2) }] };
    } catch (error: any) {
      console.error(`[ERROR] Tool 'list_root_fields' failed: ${error.message}`);
      throw error;
    }
  }

• src/index.ts:250-252 (schema)

  Zod schema for input parameters: optional 'fieldType' enum to filter by QUERY, MUTATION, or SUBSCRIPTION.

  {
    fieldType: z.enum(["QUERY", "MUTATION", "SUBSCRIPTION"]).optional().describe("Optional. Filter by 'QUERY'...")
  },