improve router prompt

apps/docs/content/docs/en/blocks/router.mdx

@@ -2,7 +2,6 @@
 title: Router
 ---
 
-import { Callout } from 'fumadocs-ui/components/callout'
 import { Tab, Tabs } from 'fumadocs-ui/components/tabs'
 import { Image } from '@/components/ui/image'
 
@@ -102,11 +101,18 @@ Input (Lead) → Router
                 └── [Self-serve] → Workflow (Automated Onboarding)
 ```
 
+## Error Handling
+
+When the Router cannot determine an appropriate route for the given context, it will route to the **error path** instead of arbitrarily selecting a route. This happens when:
+
+- The context doesn't clearly match any of the defined route descriptions
+- The AI determines that none of the available routes are appropriate
+
 ## Best Practices
 
 - **Write clear route descriptions**: Each route description should clearly explain when that route should be selected. Be specific about the criteria.
 - **Make routes mutually exclusive**: When possible, ensure route descriptions don't overlap to prevent ambiguous routing decisions.
-- **Include an error/fallback route**: Add a catch-all route for unexpected inputs that don't match other routes.
+- **Connect an error path**: Handle cases where no route matches by connecting an error handler for graceful fallback behavior.
 - **Use descriptive route titles**: Route titles appear in the workflow canvas, so make them meaningful for readability.
 - **Test with diverse inputs**: Ensure the Router handles various input types, edge cases, and unexpected content.
 - **Monitor routing performance**: Review routing decisions regularly and refine route descriptions based on actual usage patterns.

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx

@@ -654,17 +654,20 @@ export function ConditionInput({
   }
 
   const removeBlock = (id: string) => {
-    if (isPreview || disabled || conditionalBlocks.length <= 2) return
+    if (isPreview || disabled) return
+    // Condition mode requires at least 2 blocks (if/else), router mode requires at least 1
+    const minBlocks = isRouterMode ? 1 : 2
+    if (conditionalBlocks.length <= minBlocks) return
 
     // Remove any associated edges before removing the block
+    const handlePrefix = isRouterMode ? `router-${id}` : `condition-${id}`
     const edgeIdsToRemove = edges
-      .filter((edge) => edge.sourceHandle?.startsWith(`condition-${id}`))
+      .filter((edge) => edge.sourceHandle?.startsWith(handlePrefix))
       .map((edge) => edge.id)
     if (edgeIdsToRemove.length > 0) {
       batchRemoveEdges(edgeIdsToRemove)
     }
 
-    if (conditionalBlocks.length === 1) return
     shouldPersistRef.current = true
     setConditionalBlocks((blocks) => updateBlockTitles(blocks.filter((block) => block.id !== id)))
 
@@ -816,7 +819,9 @@ export function ConditionInput({
                   <Button
                     variant='ghost'
                     onClick={() => removeBlock(block.id)}
-                    disabled={isPreview || disabled || conditionalBlocks.length === 1}
+                    disabled={
+                      isPreview || disabled || conditionalBlocks.length <= (isRouterMode ? 1 : 2)
+                    }
                     className='h-auto p-0 text-[var(--text-error)] hover:text-[var(--text-error)]'
                   >
                     <Trash className='h-[14px] w-[14px]' />

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx

@@ -863,7 +863,8 @@ export const WorkflowBlock = memo(function WorkflowBlock({
           return parsed.map((item: unknown, index: number) => {
             const routeItem = item as { id?: string; value?: string }
             return {
-              id: routeItem?.id ?? `${id}-route-${index}`,
+              // Use stable ID format that matches ConditionInput's generateStableId
+              id: routeItem?.id ?? `${id}-route${index + 1}`,
               value: routeItem?.value ?? '',
             }
           })
@@ -873,7 +874,8 @@ export const WorkflowBlock = memo(function WorkflowBlock({
       logger.warn('Failed to parse router routes value', { error, blockId: id })
     }
 
-    return [{ id: `${id}-route-route1`, value: '' }]
+    // Fallback must match ConditionInput's default: generateStableId(blockId, 'route1') = `${blockId}-route1`
+    return [{ id: `${id}-route1`, value: '' }]
   }, [type, subBlockState, id])
 
   /**

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx

@@ -987,6 +987,14 @@ const WorkflowContent = React.memo(() => {
         const handleId = conditionHandles[0].getAttribute('data-handleid')
         if (handleId) return handleId
       }
+    } else if (block.type === 'router_v2') {
+      const routerHandles = document.querySelectorAll(
+        `[data-nodeid^="${block.id}"][data-handleid^="router-"]`
+      )
+      if (routerHandles.length > 0) {
+        const handleId = routerHandles[0].getAttribute('data-handleid')
+        if (handleId) return handleId
+      }
     } else if (block.type === 'loop') {
       return 'loop-end-source'
     } else if (block.type === 'parallel') {

apps/sim/blocks/blocks/router.ts

@@ -115,25 +115,26 @@ Description: ${route.value || 'No description provided'}
     )
     .join('\n')
 
-  return `You are an intelligent routing agent. Your task is to analyze the provided context and select the most appropriate route from the available options.
+  return `You are a DETERMINISTIC routing agent. You MUST select exactly ONE option.
 
 Available Routes:
 ${routesInfo}
 
-Context to analyze:
+Context to route:
 ${context}
 
-Instructions:
-1. Carefully analyze the context against each route's description
-2. Select the route that best matches the context's intent and requirements
-3. Consider the semantic meaning, not just keyword matching
-4. If multiple routes could match, choose the most specific one
+ROUTING RULES:
+1. ALWAYS prefer selecting a route over NO_MATCH
+2. Pick the route whose description BEST matches the context, even if it's not a perfect match
+3. If the context is even partially related to a route's description, select that route
+4. ONLY output NO_MATCH if the context is completely unrelated to ALL route descriptions
 
-Response Format:
-Return ONLY the route ID as a single string, no punctuation, no explanation.
-Example: "route-abc123"
+OUTPUT FORMAT:
+- Output EXACTLY one route ID (copied exactly as shown above) OR "NO_MATCH"
+- No explanation, no punctuation, no additional text
+- Just the route ID or NO_MATCH
 
-Remember: Your response must be ONLY the route ID - no additional text, formatting, or explanation.`
+Your response:`
 }
 
 /**

apps/sim/executor/handlers/router/router-handler.ts

@@ -278,14 +278,24 @@ export class RouterBlockHandler implements BlockHandler {
       const result = await response.json()
 
       const chosenRouteId = result.content.trim()
+
+      if (chosenRouteId === 'NO_MATCH' || chosenRouteId.toUpperCase() === 'NO_MATCH') {
+        logger.info('Router determined no route matches the context, routing to error path')
+        throw new Error('Router could not determine a matching route for the given context')
+      }
+
       const chosenRoute = routes.find((r) => r.id === chosenRouteId)
 
+      // Throw error if LLM returns invalid route ID - this routes through error path
       if (!chosenRoute) {
+        const availableRoutes = routes.map((r) => ({ id: r.id, title: r.title }))
         logger.error(
-          `Invalid routing decision. Response content: "${result.content}", available routes:`,
-          routes.map((r) => ({ id: r.id, title: r.title }))
+          `Invalid routing decision. Response content: "${result.content}". Available routes:`,
+          availableRoutes
+        )
+        throw new Error(
+          `Router could not determine a valid route. LLM response: "${result.content}". Available route IDs: ${routes.map((r) => r.id).join(', ')}`
         )
-        throw new Error(`Invalid routing decision: ${chosenRouteId}`)
       }
 
       // Find the target block connected to this route's handle

bun.lock

@@ -1,6 +1,5 @@
 {
   "lockfileVersion": 1,
-  "configVersion": 0,
   "workspaces": {
     "": {
       "name": "simstudio",