diff --git a/src/common/utils/tools/schemaSanitizer.test.ts b/src/common/utils/tools/schemaSanitizer.test.ts
new file mode 100644
index 0000000000..1fef411dcc
--- /dev/null
+++ b/src/common/utils/tools/schemaSanitizer.test.ts
@@ -0,0 +1,269 @@
+/* eslint-disable @typescript-eslint/no-unsafe-assignment, @typescript-eslint/no-unsafe-member-access */
+import { sanitizeToolSchemaForOpenAI, sanitizeMCPToolsForOpenAI } from "./schemaSanitizer";
+import type { Tool } from "ai";
+
+// Test helper to access tool parameters
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function getParams(tool: Tool): any {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  return (tool as any).parameters;
+}
+
+// Test helper to access tool inputSchema (MCP tools)
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function getInputSchema(tool: Tool): any {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const inputSchema = (tool as any).inputSchema;
+  // inputSchema has a jsonSchema getter
+  return inputSchema?.jsonSchema;
+}
+
+describe("schemaSanitizer", () => {
+  describe("sanitizeToolSchemaForOpenAI", () => {
+    it("should strip minLength from string properties", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            content: { type: "string", minLength: 1 },
+          },
+        },
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(sanitized);
+
+      expect(params.properties.content).toEqual({ type: "string" });
+      expect(params.properties.content.minLength).toBeUndefined();
+    });
+
+    it("should strip multiple unsupported properties", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            name: { type: "string", minLength: 1, maxLength: 100, pattern: "^[a-z]+$" },
+            age: { type: "number", minimum: 0, maximum: 150, default: 25 },
+          },
+        },
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(sanitized);
+
+      expect(params.properties.name).toEqual({ type: "string" });
+      expect(params.properties.age).toEqual({ type: "number" });
+    });
+
+    it("should handle nested objects", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            user: {
+              type: "object",
+              properties: {
+                email: { type: "string", format: "email", minLength: 5 },
+              },
+            },
+          },
+        },
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(sanitized);
+
+      expect(params.properties.user.properties.email).toEqual({ type: "string" });
+    });
+
+    it("should handle array items", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            tags: {
+              type: "array",
+              items: { type: "string", minLength: 1 },
+              minItems: 1,
+              maxItems: 10,
+            },
+          },
+        },
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(sanitized);
+
+      expect(params.properties.tags.items).toEqual({ type: "string" });
+      expect(params.properties.tags.minItems).toBeUndefined();
+      expect(params.properties.tags.maxItems).toBeUndefined();
+    });
+
+    it("should handle anyOf/oneOf schemas", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            value: {
+              oneOf: [
+                { type: "string", minLength: 1 },
+                { type: "number", minimum: 0 },
+              ],
+            },
+          },
+        },
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(sanitized);
+
+      expect(params.properties.value.oneOf[0]).toEqual({ type: "string" });
+      expect(params.properties.value.oneOf[1]).toEqual({ type: "number" });
+    });
+
+    it("should preserve required and type properties", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            content: { type: "string", minLength: 1 },
+          },
+          required: ["content"],
+        },
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(sanitized);
+
+      expect(params.type).toBe("object");
+      expect(params.required).toEqual(["content"]);
+    });
+
+    it("should return tool as-is if no parameters", () => {
+      const tool = {
+        description: "Test tool",
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(tool);
+
+      expect(sanitized).toEqual(tool);
+    });
+
+    it("should not mutate the original tool", () => {
+      const tool = {
+        description: "Test tool",
+        parameters: {
+          type: "object",
+          properties: {
+            content: { type: "string", minLength: 1 },
+          },
+        },
+      } as unknown as Tool;
+
+      sanitizeToolSchemaForOpenAI(tool);
+      const params = getParams(tool);
+
+      // Original should still have minLength
+      expect(params.properties.content.minLength).toBe(1);
+    });
+
+    it("should sanitize MCP tools with inputSchema", () => {
+      // MCP tools use inputSchema with a jsonSchema getter instead of parameters
+      const jsonSchema = {
+        type: "object",
+        properties: {
+          content: { type: "string", minLength: 1, maxLength: 100 },
+          count: { type: "number", minimum: 0, maximum: 10 },
+        },
+        required: ["content"],
+      };
+
+      const mcpTool = {
+        type: "dynamic",
+        description: "MCP test tool",
+        inputSchema: {
+          // Simulate the jsonSchema getter that @ai-sdk/mcp creates
+          get jsonSchema() {
+            return jsonSchema;
+          },
+        },
+        execute: () => Promise.resolve({}),
+      } as unknown as Tool;
+
+      const sanitized = sanitizeToolSchemaForOpenAI(mcpTool);
+      const schema = getInputSchema(sanitized);
+
+      // Unsupported properties should be stripped
+      expect(schema.properties.content).toEqual({ type: "string" });
+      expect(schema.properties.count).toEqual({ type: "number" });
+      // Supported properties should be preserved
+      expect(schema.type).toBe("object");
+      expect(schema.required).toEqual(["content"]);
+    });
+
+    it("should not mutate the original MCP tool inputSchema", () => {
+      const jsonSchema = {
+        type: "object",
+        properties: {
+          content: { type: "string", minLength: 1 },
+        },
+      };
+
+      const mcpTool = {
+        type: "dynamic",
+        description: "MCP test tool",
+        inputSchema: {
+          get jsonSchema() {
+            return jsonSchema;
+          },
+        },
+        execute: () => Promise.resolve({}),
+      } as unknown as Tool;
+
+      sanitizeToolSchemaForOpenAI(mcpTool);
+
+      // Original should still have minLength
+      expect(jsonSchema.properties.content.minLength).toBe(1);
+    });
+  });
+
+  describe("sanitizeMCPToolsForOpenAI", () => {
+    it("should sanitize all tools in a record", () => {
+      const tools = {
+        tool1: {
+          description: "Tool 1",
+          parameters: {
+            type: "object",
+            properties: {
+              content: { type: "string", minLength: 1 },
+            },
+          },
+        },
+        tool2: {
+          description: "Tool 2",
+          parameters: {
+            type: "object",
+            properties: {
+              count: { type: "number", minimum: 0 },
+            },
+          },
+        },
+      } as unknown as Record<string, Tool>;
+
+      const sanitized = sanitizeMCPToolsForOpenAI(tools);
+
+      expect(getParams(sanitized.tool1).properties.content).toEqual({
+        type: "string",
+      });
+      expect(getParams(sanitized.tool2).properties.count).toEqual({
+        type: "number",
+      });
+    });
+  });
+});
diff --git a/src/common/utils/tools/schemaSanitizer.ts b/src/common/utils/tools/schemaSanitizer.ts
new file mode 100644
index 0000000000..a5a7ad2c79
--- /dev/null
+++ b/src/common/utils/tools/schemaSanitizer.ts
@@ -0,0 +1,181 @@
+import { type Tool } from "ai";
+
+/**
+ * JSON Schema properties that are not permitted by OpenAI's Responses API.
+ *
+ * OpenAI's Structured Outputs has stricter JSON Schema validation than other providers.
+ * MCP tools may have schemas with these properties which work fine with Anthropic
+ * but fail with OpenAI. We strip these properties to ensure compatibility.
+ *
+ * @see https://platform.openai.com/docs/guides/structured-outputs
+ * @see https://github.com/vercel/ai/discussions/5164
+ */
+const OPENAI_UNSUPPORTED_SCHEMA_PROPERTIES = new Set([
+  // String validation
+  "minLength",
+  "maxLength",
+  "pattern",
+  "format",
+  // Number validation
+  "minimum",
+  "maximum",
+  "exclusiveMinimum",
+  "exclusiveMaximum",
+  "multipleOf",
+  // Array validation
+  "minItems",
+  "maxItems",
+  "uniqueItems",
+  // Object validation
+  "minProperties",
+  "maxProperties",
+  // General
+  "default",
+  "examples",
+  "deprecated",
+  "readOnly",
+  "writeOnly",
+  // Composition (partially supported - strip from items/properties)
+  // Note: oneOf/anyOf at root level may work, but not in nested contexts
+]);
+
+/**
+ * Recursively strip unsupported schema properties for OpenAI compatibility.
+ * This mutates the schema in place for efficiency.
+ */
+function stripUnsupportedProperties(schema: unknown): void {
+  if (typeof schema !== "object" || schema === null) {
+    return;
+  }
+
+  const obj = schema as Record<string, unknown>;
+
+  // Remove unsupported properties at this level
+  for (const prop of OPENAI_UNSUPPORTED_SCHEMA_PROPERTIES) {
+    if (prop in obj) {
+      delete obj[prop];
+    }
+  }
+
+  // Recursively process nested schemas
+  if (obj.properties && typeof obj.properties === "object") {
+    for (const propSchema of Object.values(obj.properties as Record<string, unknown>)) {
+      stripUnsupportedProperties(propSchema);
+    }
+  }
+
+  if (obj.items) {
+    if (Array.isArray(obj.items)) {
+      for (const itemSchema of obj.items) {
+        stripUnsupportedProperties(itemSchema);
+      }
+    } else {
+      stripUnsupportedProperties(obj.items);
+    }
+  }
+
+  if (obj.additionalProperties && typeof obj.additionalProperties === "object") {
+    stripUnsupportedProperties(obj.additionalProperties);
+  }
+
+  // Handle anyOf/oneOf/allOf
+  for (const keyword of ["anyOf", "oneOf", "allOf"]) {
+    if (Array.isArray(obj[keyword])) {
+      for (const subSchema of obj[keyword] as unknown[]) {
+        stripUnsupportedProperties(subSchema);
+      }
+    }
+  }
+
+  // Handle definitions/defs (JSON Schema draft-07 and later)
+  for (const defsKey of ["definitions", "$defs"]) {
+    if (obj[defsKey] && typeof obj[defsKey] === "object") {
+      for (const defSchema of Object.values(obj[defsKey] as Record<string, unknown>)) {
+        stripUnsupportedProperties(defSchema);
+      }
+    }
+  }
+}
+
+/**
+ * Sanitize a tool's parameter schema for OpenAI Responses API compatibility.
+ *
+ * OpenAI's Responses API has stricter JSON Schema validation than other providers.
+ * This function creates a new tool with sanitized parameters that strips
+ * unsupported schema properties like minLength, maximum, default, etc.
+ *
+ * Tools can have schemas in two places:
+ * - `parameters`: Used by tools created with ai SDK's `tool()` function
+ * - `inputSchema`: Used by MCP tools created with `dynamicTool()` from @ai-sdk/mcp
+ *
+ * @param tool - The original tool to sanitize
+ * @returns A new tool with sanitized parameter schema
+ */
+export function sanitizeToolSchemaForOpenAI(tool: Tool): Tool {
+  // Access tool internals - the AI SDK tool structure varies:
+  // - Regular tools have `parameters` (Zod schema)
+  // - MCP/dynamic tools have `inputSchema` (JSON Schema wrapper with getter)
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const toolRecord = tool as any as Record<string, unknown>;
+
+  // Check for inputSchema first (MCP tools use this)
+  // The inputSchema is a wrapper object with a jsonSchema getter
+  if (toolRecord.inputSchema && typeof toolRecord.inputSchema === "object") {
+    const inputSchemaWrapper = toolRecord.inputSchema as Record<string, unknown>;
+
+    // Get the actual JSON Schema - it's exposed via a getter
+    const rawJsonSchema = inputSchemaWrapper.jsonSchema;
+    if (rawJsonSchema && typeof rawJsonSchema === "object") {
+      // Deep clone and sanitize
+      const clonedSchema = JSON.parse(JSON.stringify(rawJsonSchema)) as Record<string, unknown>;
+      stripUnsupportedProperties(clonedSchema);
+
+      // Create a new inputSchema wrapper that returns our sanitized schema
+      const sanitizedInputSchema = {
+        ...inputSchemaWrapper,
+        // Override the jsonSchema getter with our sanitized version
+        get jsonSchema() {
+          return clonedSchema;
+        },
+      };
+
+      return {
+        ...tool,
+        inputSchema: sanitizedInputSchema,
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      } as any as Tool;
+    }
+  }
+
+  // Fall back to parameters (regular AI SDK tools)
+  if (!toolRecord.parameters) {
+    return tool;
+  }
+
+  // Deep clone the parameters to avoid mutating the original
+  const clonedParams = JSON.parse(JSON.stringify(toolRecord.parameters)) as unknown;
+
+  // Strip unsupported properties
+  stripUnsupportedProperties(clonedParams);
+
+  // Create a new tool with sanitized parameters
+  return {
+    ...tool,
+    parameters: clonedParams,
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  } as any as Tool;
+}
+
+/**
+ * Sanitize all MCP tools for OpenAI compatibility.
+ *
+ * @param mcpTools - Record of MCP tools to sanitize
+ * @returns Record of sanitized tools
+ */
+export function sanitizeMCPToolsForOpenAI(mcpTools: Record<string, Tool>): Record<string, Tool> {
+  const sanitized: Record<string, Tool> = {};
+  for (const [name, tool] of Object.entries(mcpTools)) {
+    sanitized[name] = sanitizeToolSchemaForOpenAI(tool);
+  }
+  return sanitized;
+}
diff --git a/src/common/utils/tools/tools.ts b/src/common/utils/tools/tools.ts
index e3fb536adb..55b0d8f887 100644
--- a/src/common/utils/tools/tools.ts
+++ b/src/common/utils/tools/tools.ts
@@ -13,6 +13,7 @@ import { createTodoWriteTool, createTodoReadTool } from "@/node/services/tools/t
 import { createStatusSetTool } from "@/node/services/tools/status_set";
 import { wrapWithInitWait } from "@/node/services/tools/wrapWithInitWait";
 import { log } from "@/node/services/log";
+import { sanitizeMCPToolsForOpenAI } from "@/common/utils/tools/schemaSanitizer";
 
 import type { Runtime } from "@/node/runtime/Runtime";
 import type { InitStateManager } from "@/node/services/initStateManager";
@@ -157,17 +158,29 @@ export async function getToolsForModel(
       }
 
       case "openai": {
+        // Sanitize MCP tools for OpenAI's stricter JSON Schema validation.
+        // OpenAI's Responses API doesn't support certain schema properties like
+        // minLength, maximum, default, etc. that are valid JSON Schema but not
+        // accepted by OpenAI's Structured Outputs implementation.
+        const sanitizedMcpTools = mcpTools ? sanitizeMCPToolsForOpenAI(mcpTools) : {};
+
         // Only add web search for models that support it
         if (modelId.includes("gpt-5") || modelId.includes("gpt-4")) {
           const { openai } = await import("@ai-sdk/openai");
           allTools = {
             ...baseTools,
-            ...(mcpTools ?? {}),
+            ...sanitizedMcpTools,
             // Provider-specific tool types are compatible with Tool at runtime
             web_search: openai.tools.webSearch({
               searchContextSize: "high",
             }) as Tool,
           };
+        } else {
+          // For other OpenAI models (o1, o3, etc.), still use sanitized MCP tools
+          allTools = {
+            ...baseTools,
+            ...sanitizedMcpTools,
+          };
         }
         break;
       }