diff --git a/README.md b/README.md
index f07e707..f7f29d9 100644
--- a/README.md
+++ b/README.md
@@ -55,3 +55,4 @@ Please refer to [Wiki](https://github.com/lyc8503/UptimeFlare/wiki)
 - [ ] Groups 
 - [x] Remove old incidents
 - [ ] Known issue: `fetch` doesn't support non-standard port
+- [ ] Update wiki and add docs for dev
diff --git a/uptime.config.ts b/uptime.config.ts
index acddf06..0d3edae 100644
--- a/uptime.config.ts
+++ b/uptime.config.ts
@@ -43,6 +43,8 @@ const workerConfig = {
       body: 'Hello, world!',
       // [OPTIONAL] if specified, the response must contains the keyword to be considered as operational.
       responseKeyword: 'success',
+      // [OPTIONAL] if specified, the response must NOT contains the keyword to be considered as operational.
+      responseForbiddenKeyword: 'bad gateway',
       // [OPTIONAL] if specified, the check will run in your specified region,
       // refer to docs https://github.com/lyc8503/UptimeFlare/wiki/Geo-specific-checks-setup before setting this value
       checkLocationWorkerRoute: 'https://xxx.example.com',
diff --git a/uptime.types.ts b/uptime.types.ts
index aa1748b..a4d56cd 100644
--- a/uptime.types.ts
+++ b/uptime.types.ts
@@ -43,6 +43,7 @@ type MonitorTarget = {
   headers?: Record<string, string | undefined>
   body?: BodyInit
   responseKeyword?: string
+  responseForbiddenKeyword?: string
 }
 
 export type { MonitorState, MonitorTarget }
diff --git a/worker/src/monitor.ts b/worker/src/monitor.ts
index 216c06e..d235850 100644
--- a/worker/src/monitor.ts
+++ b/worker/src/monitor.ts
@@ -72,14 +72,25 @@ export async function getStatus(
         }
       }
 
-      if (monitor.responseKeyword) {
+      if (monitor.responseKeyword || monitor.responseForbiddenKeyword) {
+        // Only read response body if we have a keyword to check
         const responseBody = await response.text()
-        if (!responseBody.includes(monitor.responseKeyword)) {
+
+        // MUST contain responseKeyword
+        if (monitor.responseKeyword && !responseBody.includes(monitor.responseKeyword)) {
           console.log(`${monitor.name} expected keyword ${monitor.responseKeyword}, not found in response (truncated to 100 chars): ${responseBody.slice(0, 100)}`)
           status.up = false
           status.err = "HTTP response doesn't contain the configured keyword"
           return status
         }
+
+        // MUST NOT contain responseForbiddenKeyword
+        if (monitor.responseForbiddenKeyword && responseBody.includes(monitor.responseForbiddenKeyword)) {
+          console.log(`${monitor.name} forbidden keyword ${monitor.responseForbiddenKeyword}, found in response (truncated to 100 chars): ${responseBody.slice(0, 100)}`)
+          status.up = false
+          status.err = "HTTP response contains the configured forbidden keyword"
+          return status
+        }
       }
 
       status.up = true