feat(workflow-as-mcp): wrapping workflows in the same workspace as MCP tools to particular MCP servers

[Pbonmars-20031006]

Summary

We wrap the existing API calls as MCP tool endpoints and use them to trigger workflows from MCP servers.

Type of Change

• New feature

Testing

Tested manually with @Sg312

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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Project	Deployment	Review	Updated (UTC)
docs	Ready	Preview, Comment	Dec 31, 2025 0:49am

[greptile-apps]

Greptile Summary

This PR implements a comprehensive MCP (Model Context Protocol) server system that wraps deployed workflows as callable tools. The implementation adds infrastructure for users to create workspace-scoped MCP servers, register deployed workflows as tools, and expose them via standard MCP protocol endpoints for external clients.

Key Changes:

• Added workflow_mcp_server and workflow_mcp_tool database tables with proper foreign keys and cascade deletes
• Implemented /api/mcp/serve/[serverId] endpoint with full JSON-RPC 2.0 MCP protocol support (initialize, tools/list, tools/call)
• Created CRUD APIs for managing workflow MCP servers and tools with workspace-level authorization
• Built automatic schema sync system that updates tool parameter schemas when workflows deploy/undeploy
• Added mcp as a new trigger type across execution logging and rate limiting systems
• Integrated workflow MCP tool management into deploy modal UI with parameter description editing
• Tool execution flows through internal workflow execute API with proper authentication and 5-minute timeout

Architecture:
The implementation maintains clear separation between external MCP servers (for consuming tools) and workflow MCP servers (for exposing workflows). Tool registration validates that workflows are deployed and have valid start blocks. Schema generation converts workflow input formats to JSON Schema and Zod schemas compatible with MCP clients.

Security:
All workflow MCP server endpoints use withMcpAuth middleware for workspace-level authorization. Tool execution uses checkHybridAuth and only executes deployed workflows. The serve endpoint accepts API keys via headers for external MCP client authentication.

Confidence Score: 4/5

• Safe to merge with one potential timeout concern in workflow execution flow
• The implementation is well-structured with proper authorization, validation, and error handling. Database schema changes are clean with appropriate constraints. The automatic schema sync is non-critical and won't break workflows if it fails. Minor concern: the serve endpoint's internal fetch to workflow execute API could potentially hang despite the 5-minute timeout if the execute endpoint itself has issues, but this is handled gracefully with error responses.
• Pay close attention to apps/sim/app/api/mcp/serve/[serverId]/route.ts for the internal API fetch timeout handling

Important Files Changed

Filename	Overview
packages/db/schema.ts	Added two new tables (workflow_mcp_server and workflow_mcp_tool) with proper foreign keys, indexes, and cascade deletes
packages/db/migrations/0134_parallel_galactus.sql	Migration creates workflow MCP tables with proper constraints and unique index on server-workflow pairs
apps/sim/lib/mcp/workflow-tool-schema.ts	Schema generation converts workflow input format to JSON Schema and Zod schemas for MCP tools
apps/sim/lib/mcp/workflow-mcp-sync.ts	Syncs MCP tool schemas when workflows deploy/undeploy, removes tools when start block removed
apps/sim/app/api/mcp/serve/[serverId]/route.ts	MCP protocol server endpoint with JSON-RPC handling, workflow execution via internal API call with 5-minute timeout
apps/sim/app/api/mcp/workflow-servers/route.ts	CRUD API for workflow MCP servers with proper workspace authorization via withMcpAuth middleware
apps/sim/app/api/mcp/workflow-servers/[id]/tools/route.ts	Tool management API validates deployed status, start block presence, and workspace membership before adding tools
apps/sim/app/api/workflows/[id]/deploy/route.ts	Integrated MCP tool sync on deploy/undeploy to keep parameter schemas updated

Sequence Diagram

sequenceDiagram
    participant Client as MCP Client
    participant ServeAPI as /api/mcp/serve/[serverId]
    participant ExecAPI as /api/workflows/[id]/execute
    participant DB as Database
    participant Workflow as Workflow Engine
    
    Note over Client,Workflow: MCP Tool Execution Flow
    
    Client->>ServeAPI: POST tools/call {name, arguments}
    ServeAPI->>ServeAPI: checkHybridAuth()
    ServeAPI->>DB: Query workflow_mcp_tool by serverId + toolName
    DB-->>ServeAPI: Return tool with workflowId
    ServeAPI->>DB: Check workflow.isDeployed
    DB-->>ServeAPI: Return deployment status
    
    alt Workflow not deployed
        ServeAPI-->>Client: Error: Workflow not deployed
    else Workflow deployed
        ServeAPI->>ExecAPI: POST /api/workflows/{workflowId}/execute<br/>{input: arguments, triggerType: 'mcp'}
        ExecAPI->>Workflow: Execute workflow with input
        Workflow-->>ExecAPI: Return execution result
        ExecAPI-->>ServeAPI: Return {success, output}
        ServeAPI-->>Client: JSONRPCResponse with result
    end
    
    Note over Client,Workflow: Tool Registration & Sync Flow
    
    participant UI as Deploy UI
    participant ToolAPI as /api/mcp/workflow-servers/[id]/tools
    participant DeployAPI as /api/workflows/[id]/deploy
    participant Sync as workflow-mcp-sync
    
    UI->>ToolAPI: POST {workflowId, toolName, description}
    ToolAPI->>DB: Verify workflow.isDeployed = true
    ToolAPI->>DB: Verify hasValidStartBlock()
    ToolAPI->>DB: Insert workflow_mcp_tool
    DB-->>ToolAPI: Return created tool
    ToolAPI-->>UI: Success
    
    Note over DeployAPI,Sync: On workflow deploy/undeploy
    DeployAPI->>Sync: syncMcpToolsForWorkflow()
    Sync->>DB: Load workflow blocks
    Sync->>Sync: Extract inputFormat from start block
    Sync->>Sync: Generate parameter schema
    Sync->>DB: Update workflow_mcp_tool.parameterSchema
    DB-->>Sync: Schema updated
    Sync-->>DeployAPI: Sync complete

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[icecrasher321]

@greptile