diff --git a/clients/web/src/test/integration/mcp/inspectorClient.test.ts b/clients/web/src/test/integration/mcp/inspectorClient.test.ts
index 78e25418..f0c85846 100644
--- a/clients/web/src/test/integration/mcp/inspectorClient.test.ts
+++ b/clients/web/src/test/integration/mcp/inspectorClient.test.ts
@@ -55,6 +55,7 @@ import type {
   FetchRequestEntryBase,
   RequestMetadata,
 } from "@inspector/core/mcp/types.js";
+import type { InspectorLogger } from "@inspector/core/logging/logger.js";
 import type { JsonValue } from "@inspector/core/json/jsonUtils.js";
 import type {
   TypedEvent,
@@ -1464,6 +1465,49 @@ describe("InspectorClient", () => {
       },
     );
 
+    it("warns with the rejected progressToken's type, never its value", async () => {
+      // This logger is persisted by real clients (the TUI writes it to
+      // `~/.mcp-inspector/auth.log`), and an invalid `progressToken` can now be
+      // an object holding credentials — so the warning must not echo it.
+      const warn = vi.fn();
+      const noop = () => {};
+      const logger: InspectorLogger = {
+        level: "warn",
+        fatal: noop,
+        error: noop,
+        warn,
+        info: noop,
+        debug: noop,
+        trace: noop,
+        silent: noop,
+        child: () => logger,
+      };
+      client = new InspectorClient(
+        {
+          type: "stdio",
+          command: serverCommand.command,
+          args: serverCommand.args,
+        },
+        {
+          environment: { transport: createTransportNode, logger },
+          progress: false,
+          defaultMetadata: {
+            progressToken: { accessToken: "sk-live-should-not-appear" },
+          },
+        },
+      );
+      await client.connect();
+      await client.listTools();
+
+      const call = warn.mock.calls.find((c) =>
+        String(c[1]).includes("progressToken"),
+      );
+      expect(call).toBeDefined();
+      expect(call![0]).toEqual({ received: "object" });
+      // Belt and braces: the secret must not appear anywhere in the record.
+      expect(JSON.stringify(warn.mock.calls)).not.toContain("sk-live");
+    });
+
     it.each([
       ["a string", "tok-1"],
       ["an integer", 7],
diff --git a/core/mcp/inspectorClient.ts b/core/mcp/inspectorClient.ts
index ecec24ef..b1d6689f 100644
--- a/core/mcp/inspectorClient.ts
+++ b/core/mcp/inspectorClient.ts
@@ -369,6 +369,16 @@ interface ToolCallRequest {
 // server can't spin a tight zero-delay loop; a successful acknowledgement resets
 // the count, and past the cap we give up (mark the stream ended) rather than
 // retry a persistently-failing re-list forever.
+/**
+ * A one-word name for a JSON value's type, for diagnostics that must not
+ * disclose the value itself.
+ */
+function describeJsonType(value: unknown): string {
+  if (value === null) return "null";
+  if (Array.isArray(value)) return "array";
+  return typeof value;
+}
+
 /**
  * Whether a `_meta.progressToken` value is one the protocol allows.
  *
@@ -1078,8 +1088,13 @@ export class InspectorClient extends InspectorClientEventTarget {
     // the request stays well-formed and simply asks for no progress. Warn,
     // because a silently dropped key the user typed is worse than a noisy one.
     if ("progressToken" in merged && !isProgressToken(merged.progressToken)) {
+      // Log the rejected value's *type*, never the value. `_meta` now carries
+      // arbitrary JSON, so an invalid `progressToken` can be an object holding
+      // credentials — and this logger is persisted by real clients (the TUI
+      // writes it to `~/.mcp-inspector/auth.log`). The type is what makes the
+      // warning actionable anyway; the value would only leak.
       this.logger.warn(
-        { progressToken: merged.progressToken },
+        { received: describeJsonType(merged.progressToken) },
         "Dropping `_meta.progressToken` — expected a string or an integer.",
       );
       delete merged.progressToken;