diff --git a/src/api/providers/base-provider.ts b/src/api/providers/base-provider.ts
index 84c8cf6fe9..64d99b3f0c 100644
--- a/src/api/providers/base-provider.ts
+++ b/src/api/providers/base-provider.ts
@@ -5,6 +5,7 @@ import type { ModelInfo } from "@roo-code/types"
 import type { ApiHandler, ApiHandlerCreateMessageMetadata } from "../index"
 import { ApiStream } from "../transform/stream"
 import { countTokens } from "../../utils/countTokens"
+import { isMcpTool } from "../../utils/mcp-name"
 
 /**
  * Base class for API providers that implements common functionality.
@@ -28,18 +29,26 @@ export abstract class BaseProvider implements ApiHandler {
 			return undefined
 		}
 
-		return tools.map((tool) =>
-			tool.type === "function"
-				? {
-						...tool,
-						function: {
-							...tool.function,
-							strict: true,
-							parameters: this.convertToolSchemaForOpenAI(tool.function.parameters),
-						},
-					}
-				: tool,
-		)
+		return tools.map((tool) => {
+			if (tool.type !== "function") {
+				return tool
+			}
+
+			// MCP tools use the 'mcp--' prefix - disable strict mode for them
+			// to preserve optional parameters from the MCP server schema
+			const isMcp = isMcpTool(tool.function.name)
+
+			return {
+				...tool,
+				function: {
+					...tool.function,
+					strict: !isMcp,
+					parameters: isMcp
+						? tool.function.parameters
+						: this.convertToolSchemaForOpenAI(tool.function.parameters),
+				},
+			}
+		})
 	}
 
 	/**
diff --git a/src/api/providers/openai-native.ts b/src/api/providers/openai-native.ts
index 762b81fc83..8f9cc2297f 100644
--- a/src/api/providers/openai-native.ts
+++ b/src/api/providers/openai-native.ts
@@ -24,6 +24,7 @@ import { getModelParams } from "../transform/model-params"
 
 import { BaseProvider } from "./base-provider"
 import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from "../index"
+import { isMcpTool } from "../../utils/mcp-name"
 
 export type OpenAiNativeModel = ReturnType<OpenAiNativeHandler["getModel"]>
 
@@ -291,13 +292,18 @@ export class OpenAiNativeHandler extends BaseProvider implements SingleCompletio
 			...(metadata?.tools && {
 				tools: metadata.tools
 					.filter((tool) => tool.type === "function")
-					.map((tool) => ({
-						type: "function",
-						name: tool.function.name,
-						description: tool.function.description,
-						parameters: ensureAllRequired(tool.function.parameters),
-						strict: true,
-					})),
+					.map((tool) => {
+						// MCP tools use the 'mcp--' prefix - disable strict mode for them
+						// to preserve optional parameters from the MCP server schema
+						const isMcp = isMcpTool(tool.function.name)
+						return {
+							type: "function",
+							name: tool.function.name,
+							description: tool.function.description,
+							parameters: isMcp ? tool.function.parameters : ensureAllRequired(tool.function.parameters),
+							strict: !isMcp,
+						}
+					}),
 			}),
 			...(metadata?.tool_choice && { tool_choice: metadata.tool_choice }),
 		}
diff --git a/src/utils/__tests__/mcp-name.spec.ts b/src/utils/__tests__/mcp-name.spec.ts
index b28c2e504c..5511893f79 100644
--- a/src/utils/__tests__/mcp-name.spec.ts
+++ b/src/utils/__tests__/mcp-name.spec.ts
@@ -1,4 +1,11 @@
-import { sanitizeMcpName, buildMcpToolName, parseMcpToolName, MCP_TOOL_SEPARATOR, MCP_TOOL_PREFIX } from "../mcp-name"
+import {
+	sanitizeMcpName,
+	buildMcpToolName,
+	parseMcpToolName,
+	isMcpTool,
+	MCP_TOOL_SEPARATOR,
+	MCP_TOOL_PREFIX,
+} from "../mcp-name"
 
 describe("mcp-name utilities", () => {
 	describe("constants", () => {
@@ -8,6 +15,29 @@ describe("mcp-name utilities", () => {
 		})
 	})
 
+	describe("isMcpTool", () => {
+		it("should return true for valid MCP tool names", () => {
+			expect(isMcpTool("mcp--server--tool")).toBe(true)
+			expect(isMcpTool("mcp--my_server--get_forecast")).toBe(true)
+		})
+
+		it("should return false for non-MCP tool names", () => {
+			expect(isMcpTool("server--tool")).toBe(false)
+			expect(isMcpTool("tool")).toBe(false)
+			expect(isMcpTool("read_file")).toBe(false)
+			expect(isMcpTool("")).toBe(false)
+		})
+
+		it("should return false for old underscore format", () => {
+			expect(isMcpTool("mcp_server_tool")).toBe(false)
+		})
+
+		it("should return false for partial prefix", () => {
+			expect(isMcpTool("mcp-server")).toBe(false)
+			expect(isMcpTool("mcp")).toBe(false)
+		})
+	})
+
 	describe("sanitizeMcpName", () => {
 		it("should return underscore placeholder for empty input", () => {
 			expect(sanitizeMcpName("")).toBe("_")
diff --git a/src/utils/mcp-name.ts b/src/utils/mcp-name.ts
index 55845d67ed..c81d5e770f 100644
--- a/src/utils/mcp-name.ts
+++ b/src/utils/mcp-name.ts
@@ -17,6 +17,16 @@ export const MCP_TOOL_SEPARATOR = "--"
  */
 export const MCP_TOOL_PREFIX = "mcp"
 
+/**
+ * Check if a tool name is an MCP tool (starts with the MCP prefix and separator).
+ *
+ * @param toolName - The tool name to check
+ * @returns true if the tool name starts with "mcp--", false otherwise
+ */
+export function isMcpTool(toolName: string): boolean {
+	return toolName.startsWith(`${MCP_TOOL_PREFIX}${MCP_TOOL_SEPARATOR}`)
+}
+
 /**
  * Sanitize a name to be safe for use in API function names.
  * This removes special characters and ensures the name starts correctly.