diff --git a/src/SwaggerDiff.AspNetCore/Extensions/SwaggerDiffExtensions.cs b/src/SwaggerDiff.AspNetCore/Extensions/SwaggerDiffExtensions.cs
index 1eab00f..c70b41f 100644
--- a/src/SwaggerDiff.AspNetCore/Extensions/SwaggerDiffExtensions.cs
+++ b/src/SwaggerDiff.AspNetCore/Extensions/SwaggerDiffExtensions.cs
@@ -74,8 +74,22 @@ public static WebApplication UseSwaggerDiff(this WebApplication app)
                     await using var stream = Assembly.GetManifestResourceStream(SwaggerDiffIndexResource);
                     if (stream != null)
                     {
+                        // Inside a Map() branch, PathBase includes the RoutePrefix.
+                        // Strip it to recover the application's actual PathBase so the
+                        // frontend can prefix API calls correctly.
+                        var branchPathBase = context.Request.PathBase.Value?.TrimEnd('/') ?? "";
+                        var normalizedPrefix = options.RoutePrefix.TrimEnd('/');
+                        var pathBase = branchPathBase.EndsWith(normalizedPrefix, StringComparison.OrdinalIgnoreCase)
+                            ? branchPathBase[..^normalizedPrefix.Length]
+                            : branchPathBase;
+                        pathBase = pathBase.TrimEnd('/');
+
+                        using var reader = new StreamReader(stream);
+                        var html = (await reader.ReadToEndAsync())
+                            .Replace("{{PATH_BASE}}", pathBase);
+
                         context.Response.ContentType = "text/html";
-                        await stream.CopyToAsync(context.Response.Body);
+                        await context.Response.WriteAsync(html);
                         return;
                     }
                 }
diff --git a/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff-tool.html b/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff-tool.html
index afba531..150fbfd 100644
--- a/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff-tool.html
+++ b/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff-tool.html
@@ -26,8 +26,13 @@
             const target = document.querySelector('.topbar .download-url-wrapper');
 
             if (target && !document.getElementById('swagger-diff-btn')) {
+                // Derive PathBase from the current URL.
+                // SwaggerUI lives at {pathBase}/swagger, so strip the swagger
+                // segment to get the application's PathBase prefix.
+                const swaggerBase = window.location.pathname.replace(/\/swagger\b.*$/, '');
+
                 const btn = document.createElement('a');
-                btn.href = '/swagger-diff';
+                btn.href = swaggerBase + '/swagger-diff';
                 btn.innerHTML = `<svg xmlns='http://www.w3.org/2000/svg' height='16' viewBox='0 0 24 24' width='16' fill='white'><path d='M0 0h24v24H0V0z' fill='none'/><path d='M15.5 14h-.79l-.28-.27C15.41 12.59 16 11.11 16 9.5 16 5.91 13.09 3 9.5 3S3 5.91 3 9.5 5.91 16 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0s.41-1.08 0-1.49L15.5 14zM5 9.5C5 7.01 7.01 5 9.5 5S14 7.01 14 9.5 11.99 14 9.5 14 5 11.99 5 9.5z'/></svg>Swagger Diff Tool`;
                 btn.className = 'swagger-diff-btn';
                 btn.id = 'swagger-diff-btn';
diff --git a/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff/index.html b/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff/index.html
index 3ee4b0b..2647df6 100644
--- a/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff/index.html
+++ b/src/SwaggerDiff.AspNetCore/wwwroot/swagger-diff/index.html
@@ -199,7 +199,7 @@
 <body>
     <div class="container">
         <div class="header-row">
-            <a href="/swagger" class="back-link">&#128281; Back to Swagger</a>
+            <a href="{{PATH_BASE}}/swagger" class="back-link">&#128281; Back to Swagger</a>
             <h2 class="title">Swagger Diff Viewer</h2>
         </div>
 
@@ -241,6 +241,9 @@ <h2 class="title">Swagger Diff Viewer</h2>
     <div id="toast" class="toast"></div>
 
     <script>
+        // PathBase injected at serve-time (empty string when no reverse proxy prefix)
+        const pathBase = '{{PATH_BASE}}';
+
         // State
         let versions = [];
         let oldVersionName = '';
@@ -268,7 +271,7 @@ <h2 class="title">Swagger Diff Viewer</h2>
 
         // Copy shareable link
         function copyLink() {
-            const url = `${window.location.origin}/swagger-diff?old=${oldVersionName}&new=${newVersionName}&mode=${mode}`;
+            const url = `${window.location.origin}${window.location.pathname}?old=${oldVersionName}&new=${newVersionName}&mode=${mode}`;
             navigator.clipboard.writeText(url)
                 .then(() => showToast('Link copied to clipboard!'));
         }
@@ -334,7 +337,7 @@ <h2 class="title">Swagger Diff Viewer</h2>
         // Fetch versions from API
         async function fetchVersions() {
             try {
-                const res = await fetch('/api-docs/versions');
+                const res = await fetch(pathBase + '/api-docs/versions');
                 const json = await res.json();
                 if (!json.isSuccess) throw new Error(json.message || 'Unable to load versions');
                 versions = json.data;
@@ -355,7 +358,7 @@ <h2 class="title">Swagger Diff Viewer</h2>
             diffContainer.style.display = 'none';
 
             try {
-                const res = await fetch('/api-docs/compare', {
+                const res = await fetch(pathBase + '/api-docs/compare', {
                     method: 'POST',
                     headers: { 'Content-Type': 'application/json' },
                     body: JSON.stringify({
