diff --git a/manifest.firefox.json b/manifest.firefox.json
index dc9888f..ae8355f 100644
--- a/manifest.firefox.json
+++ b/manifest.firefox.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.42",
+  "version": "0.9.43",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "browser_specific_settings": {
     "gecko": {
diff --git a/manifest.json b/manifest.json
index 2dec8c9..425b3ec 100644
--- a/manifest.json
+++ b/manifest.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.42",
+  "version": "0.9.43",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "permissions": [
     "storage",
diff --git a/package.json b/package.json
index 3213a9e..0baad02 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "silent-send",
-  "version": "0.9.42",
+  "version": "0.9.43",
   "private": true,
   "license": "MIT",
   "description": "Browser extension that substitutes personal data before sending to AI services",
diff --git a/src/content/content.js b/src/content/content.js
index 552fd65..0702685 100644
--- a/src/content/content.js
+++ b/src/content/content.js
@@ -50,7 +50,7 @@
     const sorted = [...maps].sort((a, b) => b.real.length - a.real.length);
 
     for (const m of sorted) {
-      if (!m.enabled || !m.real || !m.substitute) continue;
+      if (!m.enabled || !m.real?.trim() || !m.substitute?.trim()) continue;
       const escaped = esc(m.real);
       const regex = new RegExp(escaped, m.caseSensitive ? 'g' : 'gi');
       let match;
@@ -70,7 +70,7 @@
     let result = text;
     const sorted = [...maps].sort((a, b) => b.substitute.length - a.substitute.length);
     for (const m of sorted) {
-      if (!m.enabled || !m.real || !m.substitute) continue;
+      if (!m.enabled || !m.real?.trim() || !m.substitute?.trim()) continue;
       const escaped = esc(m.substitute);
       const regex = new RegExp(escaped, m.caseSensitive ? 'g' : 'gi');
       result = result.replace(regex, m.real);
@@ -825,67 +825,74 @@
   }
 
   window.__ssInterceptFetch = async function (url, options) {
-    if (!settings.enabled || !hasSubstitutions()) {
+    // Top-level guard: any unhandled error must never break the original request.
+    try {
+      if (!settings.enabled || !hasSubstitutions()) {
+        return originalFetch.call(this, url, options);
+      }
+
+      const urlStr = typeof url === 'string' ? url : url?.url || '';
+      const method = (options?.method || 'GET').toUpperCase();
+
+      // Only intercept POST/PUT/PATCH
+      if (
+        (method === 'POST' || method === 'PUT' || method === 'PATCH') &&
+        options?.body && !shouldSkipUrl(urlStr)
+      ) {
+        // FormData body — scan file uploads via DocumentScanner
+        if (options.body instanceof FormData && typeof globalThis.DocumentScanner !== 'undefined') {
+          try {
+            const scannedForm = await scanFormData(options.body);
+            if (scannedForm) {
+              options = { ...options, body: scannedForm.formData };
+              if (scannedForm.replacements.length > 0) {
+                notifySubstitutions(scannedForm.replacements);
+                console.log(
+                  `[Silent Send] Substituted ${scannedForm.replacements.length} value(s) in file upload to ${urlStr}`
+                );
+              }
+            }
+          } catch (e) {
+            console.warn('[Silent Send] FormData scan failed:', e);
+          }
+        }
+
+        // String body — JSON or raw text
+        if (typeof options.body === 'string') {
+          try {
+            // Try JSON
+            const body = JSON.parse(options.body);
+            const { modified, replacements } = processBody(body);
+
+            if (modified) {
+              options = { ...options, body: JSON.stringify(body) };
+              notifySubstitutions(replacements);
+              console.log(
+                `[Silent Send] Substituted ${replacements.length} value(s) in ${urlStr}`
+              );
+            }
+          } catch (e) {
+            // Not JSON — try raw string substitution (form data, etc.)
+            if (options.body.length > MIN_STRING_LENGTH) {
+              const result = substituteAll(options.body);
+              if (result.modified) {
+                options = { ...options, body: result.text };
+                notifySubstitutions(result.replacements);
+                console.log(
+                  `[Silent Send] Substituted ${result.replacements.length} value(s) in form body`
+                );
+              }
+            }
+          }
+        }
+      }
+
+      return originalFetch.call(this, url, options);
+    } catch (e) {
+      // Something went wrong in Silent Send — never block the original request
+      console.warn('[Silent Send] Fetch interceptor error, passing through:', e);
       return originalFetch.call(this, url, options);
     }
-
-    const urlStr = typeof url === 'string' ? url : url?.url || '';
-    const method = (options?.method || 'GET').toUpperCase();
-
-    // Only intercept POST/PUT/PATCH
-    if (
-      (method === 'POST' || method === 'PUT' || method === 'PATCH') &&
-      options?.body && !shouldSkipUrl(urlStr)
-    ) {
-      // FormData body — scan file uploads via DocumentScanner
-      if (options.body instanceof FormData && typeof globalThis.DocumentScanner !== 'undefined') {
-        try {
-          const scannedForm = await scanFormData(options.body);
-          if (scannedForm) {
-            options = { ...options, body: scannedForm.formData };
-            if (scannedForm.replacements.length > 0) {
-              notifySubstitutions(scannedForm.replacements);
-              console.log(
-                `[Silent Send] Substituted ${scannedForm.replacements.length} value(s) in file upload to ${urlStr}`
-              );
-            }
-          }
-        } catch (e) {
-          console.warn('[Silent Send] FormData scan failed:', e);
-        }
-      }
-
-      // String body — JSON or raw text
-      if (typeof options.body === 'string') {
-        try {
-          // Try JSON
-          const body = JSON.parse(options.body);
-          const { modified, replacements } = processBody(body);
-
-          if (modified) {
-            options = { ...options, body: JSON.stringify(body) };
-            notifySubstitutions(replacements);
-            console.log(
-              `[Silent Send] Substituted ${replacements.length} value(s) in ${urlStr}`
-            );
-          }
-        } catch (e) {
-          // Not JSON — try raw string substitution (form data, etc.)
-          if (options.body.length > MIN_STRING_LENGTH) {
-            const result = substituteAll(options.body);
-            if (result.modified) {
-              options = { ...options, body: result.text };
-              notifySubstitutions(result.replacements);
-              console.log(
-                `[Silent Send] Substituted ${result.replacements.length} value(s) in form body`
-              );
-            }
-          }
-        }
-      }
-    }
-
-    return originalFetch.call(this, url, options);
   };
 
   // Activate the fetch hook. If early-hook.js ran first (world: MAIN, document_start),
@@ -1130,6 +1137,7 @@
 
       for (const p of pairs) {
         const searchTerm = settings.revealMode ? p.to : p.from;
+        if (!searchTerm?.trim()) continue;
         const escaped = esc(searchTerm);
         // Add word boundaries when the term starts/ends with word chars to
         // prevent partial-word matches (e.g. "aud" inside "Claude")
diff --git a/src/lib/substitution-engine.js b/src/lib/substitution-engine.js
index f7e5fd9..d0e64ec 100644
--- a/src/lib/substitution-engine.js
+++ b/src/lib/substitution-engine.js
@@ -21,7 +21,7 @@ const SubstitutionEngine = {
     );
 
     for (const mapping of sorted) {
-      if (!mapping.enabled || !mapping.real || !mapping.substitute) continue;
+      if (!mapping.enabled || !mapping.real?.trim() || !mapping.substitute?.trim()) continue;
 
       const escaped = this._escapeRegex(mapping.real);
       const regex = new RegExp(escaped, mapping.caseSensitive ? 'g' : 'gi');
@@ -54,7 +54,7 @@ const SubstitutionEngine = {
     );
 
     for (const mapping of sorted) {
-      if (!mapping.enabled || !mapping.real || !mapping.substitute) continue;
+      if (!mapping.enabled || !mapping.real?.trim() || !mapping.substitute?.trim()) continue;
 
       const escaped = this._escapeRegex(mapping.substitute);
       const regex = new RegExp(escaped, mapping.caseSensitive ? 'g' : 'gi');
@@ -71,7 +71,7 @@ const SubstitutionEngine = {
     const found = [];
 
     for (const mapping of mappings) {
-      if (!mapping.enabled || !mapping.real) continue;
+      if (!mapping.enabled || !mapping.real?.trim()) continue;
 
       const escaped = this._escapeRegex(mapping.real);
       const regex = new RegExp(escaped, mapping.caseSensitive ? 'g' : 'gi');
@@ -103,7 +103,7 @@ const SubstitutionEngine = {
     // Collect all match positions in the original text
     const matches = [];
     for (const mapping of sorted) {
-      if (!mapping.enabled || !mapping.real || !mapping.substitute) continue;
+      if (!mapping.enabled || !mapping.real?.trim() || !mapping.substitute?.trim()) continue;
 
       const escaped = this._escapeRegex(mapping.real);
       const regex = new RegExp(escaped, mapping.caseSensitive ? 'g' : 'gi');
diff --git a/src/options/options.js b/src/options/options.js
index 313aedf..f78374a 100644
--- a/src/options/options.js
+++ b/src/options/options.js
@@ -1814,11 +1814,12 @@ async function applyBulkImport() {
     await Storage.updateProfile(profile.id, profile);
   }
 
-  // Add mappings
+  // Add mappings — skip any with blank/whitespace-only real values
   for (const m of result.mappings) {
+    if (!m.real?.trim()) continue;
     await Storage.addMapping({
-      real: m.real,
-      substitute: m.substitute || '',
+      real: m.real.trim(),
+      substitute: m.substitute?.trim() || '',
       category: m.category || 'general',
       caseSensitive: false,
     });