Omit optional fields with empty strings from tool calls

Author: olaservo

client/src/App.tsx

@@ -22,6 +22,7 @@ import { SESSION_KEYS, getServerSpecificKey } from "./lib/constants";
 import { AuthDebuggerState, EMPTY_DEBUGGER_STATE } from "./lib/auth-types";
 import { OAuthStateMachine } from "./lib/oauth-state-machine";
 import { cacheToolOutputSchemas } from "./utils/schemaUtils";
+import { cleanParams } from "./utils/paramUtils";
 import React, {
   Suspense,
   useCallback,
@@ -777,12 +778,18 @@ const App = () => {
     lastToolCallOriginTabRef.current = currentTabRef.current;
 
     try {
+      // Find the tool schema to clean parameters properly
+      const tool = tools.find(t => t.name === name);
+      const cleanedParams = tool?.inputSchema 
+        ? cleanParams(params, tool.inputSchema as any)
+        : params;
+
       const response = await sendMCPRequest(
         {
           method: "tools/call" as const,
           params: {
             name,
-            arguments: params,
+            arguments: cleanedParams,
             _meta: {
               progressToken: progressTokenRef.current++,
             },

client/src/components/ToolsTab.tsx

@@ -160,15 +160,22 @@ const ToolsTab = ({
                             name={key}
                             placeholder={prop.description}
                             value={(params[key] as string) ?? ""}
-                            onChange={(e) =>
-                              setParams({
-                                ...params,
-                                [key]:
-                                  e.target.value === ""
-                                    ? undefined
-                                    : e.target.value,
-                              })
-                            }
+                            onChange={(e) => {
+                              const value = e.target.value;
+                              if (value === "" && !required) {
+                                // Optional field cleared - set to undefined to omit from request
+                                setParams({
+                                  ...params,
+                                  [key]: undefined,
+                                });
+                              } else {
+                                // Field has value or is required - keep as string
+                                setParams({
+                                  ...params,
+                                  [key]: value,
+                                });
+                              }
+                            }}
                             className="mt-1"
                           />
                         ) : prop.type === "object" || prop.type === "array" ? (
@@ -202,10 +209,22 @@ const ToolsTab = ({
                             value={(params[key] as string) ?? ""}
                             onChange={(e) => {
                               const value = e.target.value;
-                              setParams({
-                                ...params,
-                                [key]: value === "" ? "" : Number(value),
-                              });
+                              if (value === "" && !required) {
+                                // Optional field cleared - set to undefined to omit from request
+                                setParams({
+                                  ...params,
+                                  [key]: undefined,
+                                });
+                              } else {
+                                // Field has value or is required - convert to number
+                                const num = Number(value);
+                                if (!isNaN(num) || value === "") {
+                                  setParams({
+                                    ...params,
+                                    [key]: value === "" ? "" : num,
+                                  });
+                                }
+                              }
                             }}
                             className="mt-1"
                           />

client/src/utils/__tests__/paramUtils.test.ts

@@ -0,0 +1,184 @@
+import { cleanParams } from "../paramUtils";
+import type { JsonSchemaType } from "../jsonUtils";
+
+describe("cleanParams", () => {
+  it("should preserve required fields even when empty", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: ["requiredString", "requiredNumber"],
+      properties: {
+        requiredString: { type: "string" },
+        requiredNumber: { type: "number" },
+        optionalString: { type: "string" },
+        optionalNumber: { type: "number" },
+      },
+    };
+
+    const params = {
+      requiredString: "",
+      requiredNumber: 0,
+      optionalString: "",
+      optionalNumber: undefined,
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({
+      requiredString: "",
+      requiredNumber: 0,
+      // optionalString and optionalNumber should be omitted
+    });
+  });
+
+  it("should omit optional fields with empty strings", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: [],
+      properties: {
+        optionalString: { type: "string" },
+        optionalNumber: { type: "number" },
+      },
+    };
+
+    const params = {
+      optionalString: "",
+      optionalNumber: "",
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({});
+  });
+
+  it("should omit optional fields with undefined values", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: [],
+      properties: {
+        optionalString: { type: "string" },
+        optionalNumber: { type: "number" },
+      },
+    };
+
+    const params = {
+      optionalString: undefined,
+      optionalNumber: undefined,
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({});
+  });
+
+  it("should omit optional fields with null values", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: [],
+      properties: {
+        optionalString: { type: "string" },
+        optionalNumber: { type: "number" },
+      },
+    };
+
+    const params = {
+      optionalString: null,
+      optionalNumber: null,
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({});
+  });
+
+  it("should preserve optional fields with meaningful values", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: [],
+      properties: {
+        optionalString: { type: "string" },
+        optionalNumber: { type: "number" },
+        optionalBoolean: { type: "boolean" },
+      },
+    };
+
+    const params = {
+      optionalString: "hello",
+      optionalNumber: 42,
+      optionalBoolean: false, // false is a meaningful value
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({
+      optionalString: "hello",
+      optionalNumber: 42,
+      optionalBoolean: false,
+    });
+  });
+
+  it("should handle mixed required and optional fields", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: ["requiredField"],
+      properties: {
+        requiredField: { type: "string" },
+        optionalWithValue: { type: "string" },
+        optionalEmpty: { type: "string" },
+        optionalUndefined: { type: "number" },
+      },
+    };
+
+    const params = {
+      requiredField: "",
+      optionalWithValue: "test",
+      optionalEmpty: "",
+      optionalUndefined: undefined,
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({
+      requiredField: "",
+      optionalWithValue: "test",
+    });
+  });
+
+  it("should handle schema without required array", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      properties: {
+        field1: { type: "string" },
+        field2: { type: "number" },
+      },
+    };
+
+    const params = {
+      field1: "",
+      field2: undefined,
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({});
+  });
+
+  it("should preserve zero values for numbers", () => {
+    const schema: JsonSchemaType = {
+      type: "object",
+      required: [],
+      properties: {
+        optionalNumber: { type: "number" },
+      },
+    };
+
+    const params = {
+      optionalNumber: 0,
+    };
+
+    const cleaned = cleanParams(params, schema);
+
+    expect(cleaned).toEqual({
+      optionalNumber: 0,
+    });
+  });
+});

client/src/utils/paramUtils.ts

@@ -0,0 +1,44 @@
+import type { JsonSchemaType } from "./jsonUtils";
+
+/**
+ * Cleans parameters by removing undefined, null, and empty string values for optional fields
+ * while preserving all values for required fields.
+ * 
+ * @param params - The parameters object to clean
+ * @param schema - The JSON schema defining which fields are required
+ * @returns Cleaned parameters object with optional empty fields omitted
+ */
+export function cleanParams(
+  params: Record<string, unknown>,
+  schema: JsonSchemaType
+): Record<string, unknown> {
+  const cleaned: Record<string, unknown> = {};
+  const required = schema.required || [];
+
+  for (const [key, value] of Object.entries(params)) {
+    const isFieldRequired = required.includes(key);
+
+    if (isFieldRequired) {
+      // Required fields: always include, even if empty string or falsy
+      cleaned[key] = value;
+    } else {
+      // Optional fields: only include if they have meaningful values
+      if (value !== undefined && value !== "" && value !== null) {
+        cleaned[key] = value;
+      }
+      // Empty strings, undefined, null for optional fields → omit completely
+    }
+  }
+
+  return cleaned;
+}
+
+/**
+ * Checks if a field should be set to undefined when cleared
+ * @param isRequired - Whether the field is required
+ * @param value - The current value
+ * @returns Whether to set the field to undefined
+ */
+export function shouldSetToUndefined(isRequired: boolean, value: string): boolean {
+  return !isRequired && value === "";
+}