diff --git a/apps/docs/openapi-v2-workflows.json b/apps/docs/openapi-v2-workflows.json
index 386196d06a8..aea9b3fa5c8 100644
--- a/apps/docs/openapi-v2-workflows.json
+++ b/apps/docs/openapi-v2-workflows.json
@@ -3701,7 +3701,7 @@
       "post": {
         "operationId": "executeWorkflowV2",
         "summary": "Execute workflow",
-        "description": "Run the active deployment, or set `run.source: \"manual\"` to run the saved draft. Deployed execution requires workspace read access and OAuth `api:write` scope or an API key; public deployments also allow anonymous synchronous or streamed runs. Manual runs require personal-key or OAuth write access and cannot be async.\n\nUse `async: true` for a queue receipt, or `stream: true` for SSE. For a synchronous run with both flags false, send `Accept: application/x-ndjson` for heartbeat frames and a final frame containing `data`. Timeouts return `200` with `status: \"failed\"` and `error.code: \"TIMEOUT\"`; inspect run status. See [Streaming](/workflows/deployment/api#streaming) for event formats. Input descriptions specify compatible modes; invalid combinations return `400`.\n\nSupply `X-Run-Id` to prevent duplicate execution. Reuse returns `409`, without replaying results. A `503` with `error.details.code: \"ASYNC_ENQUEUE_AMBIGUOUS\"` omits `Retry-After` because the run may already have started. Reconcile using the returned run ID; do not start another run with a new or omitted ID.\n\nOAuth scope: `api:write`.",
+        "description": "Run the active deployment, or set `run.source: \"manual\"` to run the saved draft. Deployed execution requires workspace read access and OAuth `api:write` scope or an API key; public deployments also allow anonymous synchronous or streamed runs. Manual runs require personal-key or OAuth write access and cannot be async.\n\nUse `async: true` for a queue receipt, or `stream: true` for SSE. For a synchronous run with both flags false, send `Accept: application/x-ndjson` for heartbeat frames and a final frame containing `data`. With `waitTimeoutSeconds`, a synchronous run still going when the wait elapses continues in the background and answers with its run receipt instead: `202` on a JSON response, or a closing `detached` frame on an NDJSON stream, which keeps its `200`. Timeouts return `200` with `status: \"failed\"` and `error.code: \"TIMEOUT\"`; inspect run status. See [Streaming](/workflows/deployment/api#streaming) for event formats. Input descriptions specify compatible modes; invalid combinations return `400`.\n\nSupply `X-Run-Id` to prevent duplicate execution. Reuse returns `409`, without replaying results. A `503` with `error.details.code: \"ASYNC_ENQUEUE_AMBIGUOUS\"` omits `Retry-After` because the run may already have started. Reconcile using the returned run ID; do not start another run with a new or omitted ID.\n\nOAuth scope: `api:write`.",
         "x-sim-operation": "workflows.execute",
         "x-oauth-scope": "api:write",
         "tags": ["Workflows"],
@@ -3891,7 +3891,7 @@
             }
           },
           "202": {
-            "description": "The asynchronous run was queued.",
+            "description": "The asynchronous run was queued, or the synchronous run was still running when `waitTimeoutSeconds` elapsed and continues in the background.",
             "headers": {
               "X-Run-Id": {
                 "$ref": "#/components/headers/X-Run-Id"
@@ -14267,7 +14267,7 @@
         "required": ["data"],
         "additionalProperties": false,
         "title": "Queued workflow execution response",
-        "description": "Receipt returned for an asynchronous workflow run.",
+        "description": "Receipt returned for an asynchronous workflow run, or for a synchronous run still running when `waitTimeoutSeconds` elapsed.",
         "examples": [
           {
             "data": {
diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.test.ts b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.test.ts
new file mode 100644
index 00000000000..ff78b3b6b0b
--- /dev/null
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.test.ts
@@ -0,0 +1,31 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it } from 'vitest'
+import { createFieldFromOutput } from '@/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields'
+
+describe('createFieldFromOutput', () => {
+  it.each([
+    ['untyped elements', { type: 'any' }],
+    ['primitive elements', { type: 'string' }],
+  ])('offers no child fields for an array of %s', (_, items) => {
+    const field = createFieldFromOutput('rows', { type: 'array', items })
+    expect(field.children).toBeUndefined()
+  })
+
+  it('offers the declared fields of object elements', () => {
+    const field = createFieldFromOutput('rows', {
+      type: 'array',
+      items: { type: 'object', properties: { id: { type: 'string' } } },
+    })
+    expect(field.children?.map((child) => child.name)).toEqual(['id'])
+  })
+
+  it('keeps the fields of an untyped object that has a field named items', () => {
+    const field = createFieldFromOutput('page', {
+      items: { type: 'string' },
+      total: { type: 'number' },
+    })
+    expect(field.children?.map((child) => child.name)).toEqual(['items', 'total'])
+  })
+})
diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.ts b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.ts
index f079448eea9..8a46bc6e735 100644
--- a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.ts
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.ts
@@ -12,7 +12,8 @@ const RESERVED_KEYS = new Set(['type', 'description'])
 /**
  * Checks if a property is an object type
  */
-const isObject = (prop: any): boolean => prop && typeof prop === 'object'
+const isObject = (prop: unknown): prop is Record<string, any> =>
+  prop !== null && typeof prop === 'object'
 
 /**
  * Gets a subblock value from the store
@@ -35,6 +36,11 @@ const extractChildFields = (prop: any): SchemaField[] | undefined => {
     return extractNestedFields(prop.items.properties)
   }
 
+  /** Typed elements without `properties` (strings, `any`) have no fields to reference. */
+  if (prop.type === 'array' && isObject(prop.items) && typeof prop.items.type === 'string') {
+    return undefined
+  }
+
   if (!('type' in prop)) {
     return extractNestedFields(prop)
   }
@@ -71,7 +77,7 @@ const extractNestedFields = (properties: Record<string, any>): SchemaField[] =>
 /**
  * Creates a schema field from an output definition
  */
-const createFieldFromOutput = (name: string, output: any): SchemaField => {
+export const createFieldFromOutput = (name: string, output: unknown): SchemaField => {
   const hasExplicitType = isObject(output) && typeof output.type === 'string'
   const type = hasExplicitType ? output.type : isObject(output) ? 'object' : 'string'
 
diff --git a/apps/sim/executor/utils/block-reference.test.ts b/apps/sim/executor/utils/block-reference.test.ts
index db3ee222df5..b8c2840f7d8 100644
--- a/apps/sim/executor/utils/block-reference.test.ts
+++ b/apps/sim/executor/utils/block-reference.test.ts
@@ -144,6 +144,33 @@ describe('resolveBlockReference', () => {
       expect(result).toEqual({ value: undefined, blockId: 'block-1' })
     })
 
+    it('rejects an undeclared field under a json field that declares its properties', () => {
+      const ctx = createContext({
+        blockData: { 'block-1': { result: { summary: 'hello' } } },
+        blockOutputSchemas: {
+          'block-1': { result: { type: 'json', properties: { summary: { type: 'string' } } } },
+        },
+      })
+
+      expect(resolveBlockReference('start', ['result', 'summary'], ctx)?.value).toBe('hello')
+      expect(() => resolveBlockReference('start', ['result', 'typo'], ctx)).toThrow(
+        InvalidFieldError
+      )
+    })
+
+    it('accepts an undeclared field under an open json field that declares its properties', () => {
+      const ctx = createContext({
+        blockData: { 'block-1': { result: { summary: 'hello' } } },
+        blockOutputSchemas: {
+          'block-1': {
+            result: { type: 'json', properties: { summary: { type: 'string' } }, open: true },
+          },
+        },
+      })
+
+      expect(resolveBlockReference('start', ['result', 'extra'], ctx)?.value).toBeUndefined()
+    })
+
     it('should resolve values nested under json field on executed block', () => {
       const ctx = createContext({
         blockData: { 'block-1': { result: { summary: 'hello' } } },
diff --git a/apps/sim/executor/utils/block-reference.ts b/apps/sim/executor/utils/block-reference.ts
index 2c2ccca82c2..55aea4a31c8 100644
--- a/apps/sim/executor/utils/block-reference.ts
+++ b/apps/sim/executor/utils/block-reference.ts
@@ -15,6 +15,8 @@ interface SchemaNode {
   type?: string
   description?: string
   properties?: unknown
+  /** Fields beyond `properties` are allowed, so a path past them is not checked. */
+  open?: boolean
   items?: unknown
 }
 
@@ -72,15 +74,25 @@ function getProperties(schema: unknown): Record<string, unknown> | undefined {
     : undefined
 }
 
+/** A node declaring its fields but allowing others, so a field it does not name is not an error. */
+function isOpenSchemaNode(value: unknown): boolean {
+  return asSchemaNode(value)?.open === true
+}
+
 function lookupField(schema: unknown, fieldName: string): unknown | undefined {
   if (typeof schema !== 'object' || schema === null) return undefined
   const typed = schema as Record<string, unknown>
+  const props = getProperties(schema)
+
+  /** An open node's fields are its `properties`; its own keys are schema metadata, never fields. */
+  if (isOpenSchemaNode(schema)) {
+    return props && fieldName in props ? props[fieldName] : undefined
+  }
 
   if (fieldName in typed) {
     return typed[fieldName]
   }
 
-  const props = getProperties(schema)
   if (props && fieldName in props) {
     return props[fieldName]
   }
@@ -140,7 +152,7 @@ export function isPathInSchema(schema: OutputSchema | undefined, pathParts: stri
     if (arrayMatch) {
       const [, prop] = arrayMatch
       const fieldDef = lookupField(current, prop)
-      if (!fieldDef) return false
+      if (!fieldDef) return isOpenSchemaNode(current)
 
       if (isFileType(fieldDef)) {
         const nextPart = pathParts[i + 1]
@@ -194,9 +206,10 @@ export function isPathInSchema(schema: OutputSchema | undefined, pathParts: stri
         current = itemField
         continue
       }
+      return isOpenSchemaNode(items)
     }
 
-    return false
+    return isOpenSchemaNode(current)
   }
 
   return true
diff --git a/apps/sim/lib/api/contracts/v2/openapi/workflows.ts b/apps/sim/lib/api/contracts/v2/openapi/workflows.ts
index e6bb6fe056f..b991553fb4b 100644
--- a/apps/sim/lib/api/contracts/v2/openapi/workflows.ts
+++ b/apps/sim/lib/api/contracts/v2/openapi/workflows.ts
@@ -223,7 +223,7 @@ const executeQueuedResponseSchema = documentedSchema(
   v2ExecuteWorkflowQueuedResponseSchema,
   'ExecuteWorkflowQueuedResponse',
   'Queued workflow execution response',
-  'Receipt returned for an asynchronous workflow run.',
+  'Receipt returned for an asynchronous workflow run, or for a synchronous run still running when `waitTimeoutSeconds` elapsed.',
   [QUEUED_RUN_EXAMPLE]
 )
 
@@ -1194,7 +1194,7 @@ const declaredRoutes = [
       applicationOperation: workflowOperations.execute,
       operationId: 'executeWorkflowV2',
       summary: 'Execute workflow',
-      description: `Run the active deployment, or set \`run.source: "manual"\` to run the saved draft. Deployed execution requires workspace read access and OAuth \`api:write\` scope or an API key; public deployments also allow anonymous synchronous or streamed runs. Manual runs require personal-key or OAuth write access and cannot be async.\n\nUse \`async: true\` for a queue receipt, or \`stream: true\` for SSE. For a synchronous run with both flags false, send \`Accept: application/x-ndjson\` for heartbeat frames and a final frame containing \`data\`. Timeouts return \`200\` with \`status: "failed"\` and \`error.code: "TIMEOUT"\`; inspect run status. See [Streaming](/workflows/deployment/api#streaming) for event formats. ${EXECUTE_OPTION_CONSTRAINTS}\n\nSupply \`X-Run-Id\` to prevent duplicate execution. Reuse returns \`409\`, without replaying results. A \`503\` with \`error.details.code: "ASYNC_ENQUEUE_AMBIGUOUS"\` omits \`Retry-After\` because the run may already have started. Reconcile using the returned run ID; do not start another run with a new or omitted ID.`,
+      description: `Run the active deployment, or set \`run.source: "manual"\` to run the saved draft. Deployed execution requires workspace read access and OAuth \`api:write\` scope or an API key; public deployments also allow anonymous synchronous or streamed runs. Manual runs require personal-key or OAuth write access and cannot be async.\n\nUse \`async: true\` for a queue receipt, or \`stream: true\` for SSE. For a synchronous run with both flags false, send \`Accept: application/x-ndjson\` for heartbeat frames and a final frame containing \`data\`. With \`waitTimeoutSeconds\`, a synchronous run still going when the wait elapses continues in the background and answers with its run receipt instead: \`202\` on a JSON response, or a closing \`detached\` frame on an NDJSON stream, which keeps its \`200\`. Timeouts return \`200\` with \`status: "failed"\` and \`error.code: "TIMEOUT"\`; inspect run status. See [Streaming](/workflows/deployment/api#streaming) for event formats. ${EXECUTE_OPTION_CONSTRAINTS}\n\nSupply \`X-Run-Id\` to prevent duplicate execution. Reuse returns \`409\`, without replaying results. A \`503\` with \`error.details.code: "ASYNC_ENQUEUE_AMBIGUOUS"\` omits \`Retry-After\` because the run may already have started. Reconcile using the returned run ID; do not start another run with a new or omitted ID.`,
       errors: [
         'BadRequest',
         'Unauthorized',
@@ -1218,7 +1218,8 @@ const declaredRoutes = [
             additionalContentTypes: ['application/x-ndjson', 'text/event-stream'],
           },
           202: {
-            description: 'The asynchronous run was queued.',
+            description:
+              'The asynchronous run was queued, or the synchronous run was still running when `waitTimeoutSeconds` elapsed and continues in the background.',
             headers: ['X-Run-Id', ...RATE_LIMIT_HEADERS],
           },
         },
diff --git a/apps/sim/lib/api/mcp/generated/v2-operations.ts b/apps/sim/lib/api/mcp/generated/v2-operations.ts
index f56b0e612f6..37f3dca65ef 100644
--- a/apps/sim/lib/api/mcp/generated/v2-operations.ts
+++ b/apps/sim/lib/api/mcp/generated/v2-operations.ts
@@ -1246,7 +1246,7 @@ export const V2_MCP_OPERATIONS = {
     contract: v2ExecuteWorkflowContract,
     summary: 'Execute workflow',
     description:
-      'Run the active deployment, or set `run.source: "manual"` to run the saved draft. Deployed execution requires workspace read access and OAuth `api:write` scope or an API key; public deployments also allow anonymous synchronous or streamed runs. Manual runs require personal-key or OAuth write access and cannot be async.\n\nUse `async: true` for a queue receipt, or `stream: true` for SSE. For a synchronous run with both flags false, send `Accept: application/x-ndjson` for heartbeat frames and a final frame containing `data`. Timeouts return `200` with `status: "failed"` and `error.code: "TIMEOUT"`; inspect run status. See [Streaming](/workflows/deployment/api#streaming) for event formats. Input descriptions specify compatible modes; invalid combinations return `400`.\n\nSupply `X-Run-Id` to prevent duplicate execution. Reuse returns `409`, without replaying results. A `503` with `error.details.code: "ASYNC_ENQUEUE_AMBIGUOUS"` omits `Retry-After` because the run may already have started. Reconcile using the returned run ID; do not start another run with a new or omitted ID.\n\nOAuth scope: `api:write`.',
+      'Run the active deployment, or set `run.source: "manual"` to run the saved draft. Deployed execution requires workspace read access and OAuth `api:write` scope or an API key; public deployments also allow anonymous synchronous or streamed runs. Manual runs require personal-key or OAuth write access and cannot be async.\n\nUse `async: true` for a queue receipt, or `stream: true` for SSE. For a synchronous run with both flags false, send `Accept: application/x-ndjson` for heartbeat frames and a final frame containing `data`. With `waitTimeoutSeconds`, a synchronous run still going when the wait elapses continues in the background and answers with its run receipt instead: `202` on a JSON response, or a closing `detached` frame on an NDJSON stream, which keeps its `200`. Timeouts return `200` with `status: "failed"` and `error.code: "TIMEOUT"`; inspect run status. See [Streaming](/workflows/deployment/api#streaming) for event formats. Input descriptions specify compatible modes; invalid combinations return `400`.\n\nSupply `X-Run-Id` to prevent duplicate execution. Reuse returns `409`, without replaying results. A `503` with `error.details.code: "ASYNC_ENQUEUE_AMBIGUOUS"` omits `Retry-After` because the run may already have started. Reconcile using the returned run ID; do not start another run with a new or omitted ID.\n\nOAuth scope: `api:write`.',
     handler: () =>
       import('@/app/api/v2/workflows/[workflowId]/execute/route').then((route) => route.POST),
   },
diff --git a/apps/sim/lib/mcp/output-schema.ts b/apps/sim/lib/mcp/output-schema.ts
index 397785d73c3..23c7e2c5249 100644
--- a/apps/sim/lib/mcp/output-schema.ts
+++ b/apps/sim/lib/mcp/output-schema.ts
@@ -1,4 +1,4 @@
-import { isRecordLike } from '@sim/utils/object'
+import { isRecordLike, toRecord } from '@sim/utils/object'
 import type { McpToolSchema } from '@/lib/mcp/types'
 
 /**
@@ -15,15 +15,21 @@ const MAX_SHAPE_DEPTH = 8
 const MAX_SHAPE_NODES = 500
 
 /**
- * The structure of a declared output schema: types, properties and array items
- * only. Descriptions, enums and examples are dropped because the snapshot is a
- * block input, and the executor and lint read every string in a block's inputs
- * as a possible `<block.path>` reference.
+ * The structure of a declared output schema: types, properties, openness and
+ * array items only. Descriptions, enums and examples are dropped because the
+ * snapshot is a block input, and the executor and lint read every string in a
+ * block's inputs as a possible `<block.path>` reference.
  */
 export interface McpToolOutputShape {
   type: 'object' | 'array' | 'string' | 'number' | 'boolean' | 'any'
-  /** Declared fields of a closed object; absent when the object is open or undeclared. */
+  /** Declared fields of an object; absent when it declares none, which leaves every field allowed. */
   properties?: Record<string, McpToolOutputShape>
+  /**
+   * The object allows fields beyond `properties`, as JSON Schema reads any object
+   * not declaring `additionalProperties: false`. A snapshot saved before this was
+   * recorded lacks it and stays closed until the operation is picked again.
+   */
+  open?: true
   items?: McpToolOutputShape
 }
 
@@ -67,23 +73,28 @@ function reduceNode(node: unknown, depth: number, budget: { nodes: number }): Mc
 
   switch (declaredType(node)) {
     case 'object': {
-      const open =
-        (node.additionalProperties !== undefined && node.additionalProperties !== false) ||
-        node.patternProperties !== undefined
-      if (open || !isRecordLike(node.properties)) return { type: 'object' }
+      const closed = node.additionalProperties === false && node.patternProperties === undefined
+      if (!closed && !isRecordLike(node.properties)) return { type: 'object' }
       const entries: [string, McpToolOutputShape][] = []
-      for (const [name, child] of Object.entries(node.properties)) {
-        /** Past the budget the object stays open: any field resolves, none is saved. */
+      for (const [name, child] of Object.entries(toRecord(node.properties))) {
+        /** Past the budget the object is saved untyped: any field resolves, none is declared. */
         if (budget.nodes <= 0) return { type: 'object' }
         entries.push([name, reduceNode(child, depth + 1, budget)])
       }
-      /** `fromEntries` keeps every declared name, `__proto__` included, as an own field. */
-      return { type: 'object', properties: Object.fromEntries(entries) }
+      return {
+        type: 'object',
+        /** `fromEntries` keeps every declared name, `__proto__` included, as an own field. */
+        properties: Object.fromEntries(entries),
+        ...(!closed && { open: true }),
+      }
     }
     case 'array':
-      return isRecordLike(node.items)
-        ? { type: 'array', items: reduceNode(node.items, depth + 1, budget) }
-        : { type: 'array' }
+      return {
+        type: 'array',
+        items: isRecordLike(node.items)
+          ? reduceNode(node.items, depth + 1, budget)
+          : { type: 'any' },
+      }
     case 'string':
       return { type: 'string' }
     case 'number':
@@ -139,6 +150,7 @@ function isShape(value: unknown, depth = 0): value is McpToolOutputShape {
     return false
   }
   if (depth > MAX_SHAPE_DEPTH + 1) return false
+  if (value.open !== undefined && value.open !== true) return false
   if (value.items !== undefined && !isShape(value.items, depth + 1)) return false
   if (value.properties === undefined) return true
   return (
diff --git a/apps/sim/lib/workflows/blocks/outputs.ts b/apps/sim/lib/workflows/blocks/outputs.ts
index 5b9eee3a3a1..24a44465568 100644
--- a/apps/sim/lib/workflows/blocks/outputs.ts
+++ b/apps/sim/lib/workflows/blocks/outputs.ts
@@ -437,6 +437,8 @@ export function getEvaluatorMetricOutputs(
 interface DeclaredOutputNode {
   type: PrimitiveValueType
   properties?: Record<string, DeclaredOutputNode>
+  /** Fields beyond `properties` are allowed: a reference to one checks like any `json` path. */
+  open?: true
   items?: DeclaredOutputNode
 }
 
@@ -449,6 +451,7 @@ function toOutputNode(shape: McpToolOutputShape): DeclaredOutputNode {
             properties: Object.fromEntries(
               Object.entries(shape.properties).map(([name, child]) => [name, toOutputNode(child)])
             ),
+            ...(shape.open && { open: true }),
           }
         : { type: 'json' }
     case 'array':
diff --git a/apps/sim/lib/workflows/editing/dangling-refs.test.ts b/apps/sim/lib/workflows/editing/dangling-refs.test.ts
index 5cec70c9f84..b7ca5986587 100644
--- a/apps/sim/lib/workflows/editing/dangling-refs.test.ts
+++ b/apps/sim/lib/workflows/editing/dangling-refs.test.ts
@@ -284,8 +284,13 @@ describe('collectDanglingBlockOutputReferences', () => {
       type: 'object' as const,
       properties: {
         role: { type: 'string' },
-        person: { type: 'object', properties: { id: { type: 'string' } } },
+        person: {
+          type: 'object',
+          properties: { id: { type: 'string' } },
+          additionalProperties: false,
+        },
       },
+      additionalProperties: false,
     }
 
     function mcpGraph(
@@ -366,7 +371,11 @@ describe('collectDanglingBlockOutputReferences', () => {
             type: 'array',
             items: {
               type: 'array',
-              items: { type: 'object', properties: { id: { type: 'string' } } },
+              items: {
+                type: 'object',
+                properties: { id: { type: 'string' } },
+                additionalProperties: false,
+              },
             },
           },
         },
@@ -382,6 +391,35 @@ describe('collectDanglingBlockOutputReferences', () => {
       expect(finding?.reason).toContain('Declared fields: structuredContent.rows.id')
     })
 
+    it('accepts an undeclared field of an object the schema leaves open', () => {
+      const open = createMcpToolOutputSnapshot('server-1', 'on_call', {
+        type: 'object',
+        properties: {
+          role: { type: 'string' },
+          person: { type: 'object', properties: { id: { type: 'string' } } },
+        },
+        additionalProperties: false,
+      })
+      expect(
+        collectDanglingBlockOutputReferences(
+          mcpGraph('<oncall.structuredContent.person.email>', open)
+        )
+      ).toEqual([])
+    })
+
+    it('accepts a path inside the elements of an array that declares no items', () => {
+      const untypedItems = createMcpToolOutputSnapshot('server-1', 'on_call', {
+        type: 'object',
+        properties: { rows: { type: 'array' } },
+        additionalProperties: false,
+      })
+      expect(
+        collectDanglingBlockOutputReferences(
+          mcpGraph('<oncall.structuredContent.rows.0.id>', untypedItems)
+        )
+      ).toEqual([])
+    })
+
     it('keeps flagging structuredContent when the operation declares no schema', () => {
       for (const snapshot of [
         undefined,
diff --git a/apps/sim/serializer/mcp-output-schema.test.ts b/apps/sim/serializer/mcp-output-schema.test.ts
index 23f4585e01b..027a8cacdc3 100644
--- a/apps/sim/serializer/mcp-output-schema.test.ts
+++ b/apps/sim/serializer/mcp-output-schema.test.ts
@@ -82,8 +82,79 @@ describe('MCP block output typed from a declared output schema', () => {
     expect(resolve(declared, ['structuredContent', 'nickname'])).toBeUndefined()
   })
 
-  it('fails a reference to a field the schema does not declare', () => {
-    expect(() => resolve(declared, ['structuredContent', 'onCall'])).toThrow(InvalidFieldError)
+  it('fails a reference to a field a closed schema does not declare', () => {
+    const closed = createMcpToolOutputSnapshot('server-1', 'on_call', {
+      ...ON_CALL_SCHEMA,
+      additionalProperties: false,
+    })
+    expect(() => resolve(closed, ['structuredContent', 'onCall'])).toThrow(InvalidFieldError)
+    expect(resolve(closed, ['structuredContent', 'role'])).toBe('sales-ops')
+  })
+
+  it('resolves an undeclared field of an object that does not close itself to empty', () => {
+    expect(resolve(declared, ['structuredContent', 'onCall'])).toBeUndefined()
+    expect(resolve(declared, ['structuredContent', 'person', 'email'])).toBeUndefined()
+  })
+
+  it('keeps the declared fields of an explicitly open object and accepts others', () => {
+    const open = createMcpToolOutputSnapshot('server-1', 'on_call', {
+      ...ON_CALL_SCHEMA,
+      additionalProperties: { type: 'string' },
+    })
+    const schema = getBlockSchema(serializeMcpBlock(open))
+    expect(schema?.structuredContent).toMatchObject({
+      properties: { role: { type: 'string' }, person: { type: 'json' } },
+    })
+    expect(resolve(open, ['structuredContent', 'role'])).toBe('sales-ops')
+    expect(resolve(open, ['structuredContent', 'onCall'])).toBeUndefined()
+  })
+
+  it('resolves a path inside the elements of an array that declares no items', () => {
+    const untypedItems = createMcpToolOutputSnapshot('server-1', 'on_call', {
+      type: 'object',
+      properties: { rows: { type: 'array' } },
+      additionalProperties: false,
+    })
+    expect(resolve(untypedItems, ['structuredContent', 'rows', '0', 'id'])).toBeUndefined()
+  })
+
+  it('checks a declared field named like the openness flag as a field', () => {
+    const named = (additionalProperties?: false) =>
+      createMcpToolOutputSnapshot('server-1', 'on_call', {
+        type: 'object',
+        properties: {
+          open: {
+            type: 'object',
+            properties: { id: { type: 'string' } },
+            ...(additionalProperties === false && { additionalProperties }),
+          },
+        },
+        ...(additionalProperties === false && { additionalProperties }),
+      })
+    expect(resolve(named(), ['structuredContent', 'open', 'id'])).toBeUndefined()
+    expect(resolve(named(), ['structuredContent', 'open', 'extra'])).toBeUndefined()
+    expect(resolve(named(false), ['structuredContent', 'open', 'id'])).toBeUndefined()
+    expect(() => resolve(named(false), ['structuredContent', 'open', 'extra'])).toThrow(
+      InvalidFieldError
+    )
+  })
+
+  it('rejects any field of a closed object that declares none', () => {
+    const empty = createMcpToolOutputSnapshot('server-1', 'on_call', {
+      type: 'object',
+      additionalProperties: false,
+    })
+    expect(() => resolve(empty, ['structuredContent', 'onCall'])).toThrow(InvalidFieldError)
+  })
+
+  it('keeps a snapshot saved before openness was recorded closed until it is retaken', () => {
+    const legacy = {
+      server: 'server-1',
+      tool: 'on_call',
+      schema: { type: 'object', properties: { role: { type: 'string' } } },
+    }
+    expect(resolve(legacy, ['structuredContent', 'role'])).toBe('sales-ops')
+    expect(() => resolve(legacy, ['structuredContent', 'onCall'])).toThrow(InvalidFieldError)
   })
 
   it('keeps content as declared alongside the typed output', () => {
diff --git a/scripts/check-explicit-any.baseline.json b/scripts/check-explicit-any.baseline.json
index b8b4e30d6ec..ca374a5b8da 100644
--- a/scripts/check-explicit-any.baseline.json
+++ b/scripts/check-explicit-any.baseline.json
@@ -63,7 +63,7 @@
     "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/types.ts": 2,
     "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/utils.ts": 2,
     "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx": 1,
-    "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.ts": 7,
+    "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-block-output-fields.ts": 6,
     "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-node-utilities.ts": 1,
     "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-scroll-management.ts": 1,
     "apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-wand.ts": 1,