diff --git a/server/src/app.ts b/server/src/app.ts
index 356d07d9..d0f38a31 100644
--- a/server/src/app.ts
+++ b/server/src/app.ts
@@ -8,6 +8,7 @@ import { createAgentRoutes } from "./agents/routes";
 import {
   type AuditReader,
   type AuditStore,
+  AuditQueryError,
   auditQueryFromUrl,
   recordAuditEvent,
 } from "./audit";
@@ -456,9 +457,16 @@ export function createApp(
       return context.json({ error: "Audit logging is not configured." }, 503);
     }
 
-    return context.json(
-      await auditReader.list(auditQueryFromUrl(new URL(context.req.url))),
-    );
+    try {
+      return context.json(
+        await auditReader.list(auditQueryFromUrl(new URL(context.req.url))),
+      );
+    } catch (error) {
+      if (error instanceof AuditQueryError) {
+        return context.json({ error: error.message }, 400);
+      }
+      throw error;
+    }
   });
   /*
    * Who is here, and what they may do.
diff --git a/server/src/audit.ts b/server/src/audit.ts
index 3e42b2b3..e057138d 100644
--- a/server/src/audit.ts
+++ b/server/src/audit.ts
@@ -579,16 +579,33 @@ export function createAuditReader(database: Database): AuditReader {
   };
 }
 
+export class AuditQueryError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "AuditQueryError";
+  }
+}
+
 export function auditQueryFromUrl(url: URL): AuditEventQuery {
-  const requestedLimit = Number.parseInt(
-    url.searchParams.get("limit") ?? "50",
-    10,
-  );
+  const rawLimit = url.searchParams.get("limit") ?? "50";
+  const trimmedLimit = rawLimit.trim();
+  const requestedLimit = /^\d+$/.test(trimmedLimit)
+    ? Number.parseInt(trimmedLimit, 10)
+    : Number.NaN;
   const limit = Number.isFinite(requestedLimit)
     ? Math.min(Math.max(requestedLimit, 1), 100)
     : 50;
   const optional = (name: string) => url.searchParams.get(name) ?? undefined;
 
+  const from = optional("from");
+  if (from !== undefined && Number.isNaN(Date.parse(from))) {
+    throw new AuditQueryError('Query parameter "from" must be a valid date.');
+  }
+  const to = optional("to");
+  if (to !== undefined && Number.isNaN(Date.parse(to))) {
+    throw new AuditQueryError('Query parameter "to" must be a valid date.');
+  }
+
   return {
     cursor: optional("cursor"),
     limit,
@@ -596,7 +613,7 @@ export function auditQueryFromUrl(url: URL): AuditEventQuery {
     actorUserId: optional("actorUserId"),
     targetType: optional("targetType"),
     targetId: optional("targetId"),
-    from: optional("from"),
-    to: optional("to"),
+    from,
+    to,
   };
 }