Fal.ai MCP Server

Instructions

Implementation Reference

• src/index.ts:324-363 (handler)

  Switch case handling the execution of the 'run_workflow' tool. Parses input using RunWorkflowSchema, calls fal.stream or fal.subscribe on the workflow_id with input params, collects stream events or full result, and returns as formatted text content.

  case "run_workflow": {
    const params = RunWorkflowSchema.parse(args);
    
    if (params.stream) {
      const stream = await fal.stream(params.workflow_id, {
        input: params.input,
      });
      
      const events: any[] = [];
      for await (const event of stream) {
        events.push({
          type: event.type,
          data: event.data,
        });
      }
      
      return {
        content: [
          {
            type: "text",
            text: JSON.stringify(events, null, 2),
          },
        ],
      };
    } else {
      const result = await fal.subscribe(params.workflow_id, {
        input: params.input,
        logs: true,
      });
      
      return {
        content: [
          {
            type: "text",
            text: JSON.stringify(result, null, 2),
          },
        ],
      };
    }
  }

• src/index.ts:77-81 (schema)

  Zod schema defining the input parameters for the run_workflow tool: workflow_id (required string), input (object), stream (optional boolean).

  const RunWorkflowSchema = z.object({
    workflow_id: z.string().describe("The workflow ID (e.g., 'workflows/fal-ai/sdxl-sticker')"),
    input: z.record(z.any()).describe("Input parameters for the workflow"),
    stream: z.boolean().default(false).optional().describe("Whether to stream workflow events"),
  });

• src/index.ts:161-183 (registration)

  Tool registration in the ListTools response, including name, description, and JSON inputSchema matching the Zod schema.

  {
    name: "run_workflow",
    description: "Run a Fal.ai workflow (e.g., sdxl-sticker pipeline)",
    inputSchema: {
      type: "object",
      properties: {
        workflow_id: {
          type: "string",
          description: "The workflow ID",
        },
        input: {
          type: "object",
          description: "Input parameters for the workflow",
        },
        stream: {
          type: "boolean",
          description: "Whether to stream workflow events",
          default: false,
        },
      },
      required: ["workflow_id", "input"],
    },
  },