diff --git a/apps/sim/executor/variables/resolvers/block.test.ts b/apps/sim/executor/variables/resolvers/block.test.ts
index 83e6cf1a73..dac00ee0b0 100644
--- a/apps/sim/executor/variables/resolvers/block.test.ts
+++ b/apps/sim/executor/variables/resolvers/block.test.ts
@@ -6,10 +6,14 @@ import type { ResolutionContext } from './reference'
 
 vi.mock('@sim/logger', () => loggerMock)
 
-/**
- * Creates a minimal workflow for testing.
- */
-function createTestWorkflow(blocks: Array<{ id: string; name?: string; type?: string }> = []) {
+function createTestWorkflow(
+  blocks: Array<{
+    id: string
+    name?: string
+    type?: string
+    outputs?: Record<string, any>
+  }> = []
+) {
   return {
     version: '1.0',
     blocks: blocks.map((b) => ({
@@ -17,7 +21,7 @@ function createTestWorkflow(blocks: Array<{ id: string; name?: string; type?: st
       position: { x: 0, y: 0 },
       config: { tool: b.type ?? 'function', params: {} },
       inputs: {},
-      outputs: {},
+      outputs: b.outputs ?? {},
       metadata: { id: b.type ?? 'function', name: b.name ?? b.id },
       enabled: true,
     })),
@@ -126,7 +130,7 @@ describe('BlockResolver', () => {
       expect(resolver.resolve('<source.items.1.id>', ctx)).toBe(2)
     })
 
-    it.concurrent('should return undefined for non-existent path', () => {
+    it.concurrent('should return undefined for non-existent path when no schema defined', () => {
       const workflow = createTestWorkflow([{ id: 'source' }])
       const resolver = new BlockResolver(workflow)
       const ctx = createTestContext('current', {
@@ -136,6 +140,48 @@ describe('BlockResolver', () => {
       expect(resolver.resolve('<source.nonexistent>', ctx)).toBeUndefined()
     })
 
+    it.concurrent('should throw error for path not in output schema', () => {
+      const workflow = createTestWorkflow([
+        {
+          id: 'source',
+          outputs: {
+            validField: { type: 'string', description: 'A valid field' },
+            nested: {
+              child: { type: 'number', description: 'Nested child' },
+            },
+          },
+        },
+      ])
+      const resolver = new BlockResolver(workflow)
+      const ctx = createTestContext('current', {
+        source: { validField: 'value', nested: { child: 42 } },
+      })
+
+      expect(() => resolver.resolve('<source.invalidField>', ctx)).toThrow(
+        /"invalidField" doesn't exist on block "source"/
+      )
+      expect(() => resolver.resolve('<source.invalidField>', ctx)).toThrow(/Available fields:/)
+    })
+
+    it.concurrent('should return undefined for path in schema but missing in data', () => {
+      const workflow = createTestWorkflow([
+        {
+          id: 'source',
+          outputs: {
+            requiredField: { type: 'string', description: 'Always present' },
+            optionalField: { type: 'string', description: 'Sometimes missing' },
+          },
+        },
+      ])
+      const resolver = new BlockResolver(workflow)
+      const ctx = createTestContext('current', {
+        source: { requiredField: 'value' },
+      })
+
+      expect(resolver.resolve('<source.requiredField>', ctx)).toBe('value')
+      expect(resolver.resolve('<source.optionalField>', ctx)).toBeUndefined()
+    })
+
     it.concurrent('should return undefined for non-existent block', () => {
       const workflow = createTestWorkflow([{ id: 'existing' }])
       const resolver = new BlockResolver(workflow)
diff --git a/apps/sim/executor/variables/resolvers/block.ts b/apps/sim/executor/variables/resolvers/block.ts
index 4c46b0d299..7786a27d6d 100644
--- a/apps/sim/executor/variables/resolvers/block.ts
+++ b/apps/sim/executor/variables/resolvers/block.ts
@@ -9,14 +9,75 @@ import {
   type ResolutionContext,
   type Resolver,
 } from '@/executor/variables/resolvers/reference'
-import type { SerializedWorkflow } from '@/serializer/types'
+import type { SerializedBlock, SerializedWorkflow } from '@/serializer/types'
+
+function isPathInOutputSchema(
+  outputs: Record<string, any> | undefined,
+  pathParts: string[]
+): boolean {
+  if (!outputs || pathParts.length === 0) {
+    return true
+  }
+
+  let current: any = outputs
+  for (let i = 0; i < pathParts.length; i++) {
+    const part = pathParts[i]
+
+    if (/^\d+$/.test(part)) {
+      continue
+    }
+
+    if (current === null || current === undefined) {
+      return false
+    }
+
+    if (part in current) {
+      current = current[part]
+      continue
+    }
+
+    if (current.properties && part in current.properties) {
+      current = current.properties[part]
+      continue
+    }
+
+    if (current.type === 'array' && current.items) {
+      if (current.items.properties && part in current.items.properties) {
+        current = current.items.properties[part]
+        continue
+      }
+      if (part in current.items) {
+        current = current.items[part]
+        continue
+      }
+    }
+
+    if ('type' in current && typeof current.type === 'string') {
+      if (!current.properties && !current.items) {
+        return false
+      }
+    }
+
+    return false
+  }
+
+  return true
+}
+
+function getSchemaFieldNames(outputs: Record<string, any> | undefined): string[] {
+  if (!outputs) return []
+  return Object.keys(outputs)
+}
 
 export class BlockResolver implements Resolver {
   private nameToBlockId: Map<string, string>
+  private blockById: Map<string, SerializedBlock>
 
   constructor(private workflow: SerializedWorkflow) {
     this.nameToBlockId = new Map()
+    this.blockById = new Map()
     for (const block of workflow.blocks) {
+      this.blockById.set(block.id, block)
       if (block.metadata?.name) {
         this.nameToBlockId.set(normalizeName(block.metadata.name), block.id)
       }
@@ -47,7 +108,9 @@ export class BlockResolver implements Resolver {
       return undefined
     }
 
+    const block = this.blockById.get(blockId)
     const output = this.getBlockOutput(blockId, context)
+
     if (output === undefined) {
       return undefined
     }
@@ -63,9 +126,6 @@ export class BlockResolver implements Resolver {
       return result
     }
 
-    // If failed, check if we should try backwards compatibility fallback
-    const block = this.workflow.blocks.find((b) => b.id === blockId)
-
     // Response block backwards compatibility:
     // Old: <responseBlock.response.data> -> New: <responseBlock.data>
     // Only apply fallback if:
@@ -108,6 +168,14 @@ export class BlockResolver implements Resolver {
       }
     }
 
+    const schemaFields = getSchemaFieldNames(block?.outputs)
+    if (schemaFields.length > 0 && !isPathInOutputSchema(block?.outputs, pathParts)) {
+      throw new Error(
+        `"${pathParts.join('.')}" doesn't exist on block "${blockName}". ` +
+          `Available fields: ${schemaFields.join(', ')}`
+      )
+    }
+
     return undefined
   }