diff --git a/AGENTS.md b/AGENTS.md
index 5eda851..1693650 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -88,6 +88,7 @@ All detection modules follow the same pattern:
 - Priority order: netlify → edge-light → workerd → fastly → deno → bun → node
 - Uses global objects (e.g., `globalThis.Bun`, `globalThis.Deno`, `navigator.userAgent`)
 - `isNode` is true for Node-compatible runtimes (Bun, Deno with compat); use `runtime === "node"` for strict check
+- `isNub` (`!!process.versions.nub`) detects [Nub](https://github.com/nubjs/nub), a Node.js augmentation layer — additive, so `isNode` stays true and `runtime` stays `"node"`; it is deliberately NOT in `runtimeChecks` or `RuntimeName`
 
 ### Flags (`src/flags.ts`)
 
diff --git a/README.md b/README.md
index f6cb308..5b3492b 100644
--- a/README.md
+++ b/README.md
@@ -17,10 +17,12 @@ console.log(runtime); // "" | "node" | "deno" | "bun" | "workerd" ...
 console.log(runtimeInfo); // { name: "node" }
 ```
 
-Individual named exports: `isNode`, `isBun`, `isDeno`, `isNetlify`, `isEdgeLight`, `isWorkerd`, `isFastly`
+Individual named exports: `isNode`, `isBun`, `isDeno`, `isNetlify`, `isEdgeLight`, `isWorkerd`, `isFastly`, `isNub`
 
 > [!NOTE]
 > `isNode` is also `true` in Bun/Deno with Node.js compatibility mode. Use `runtime === "node"` for strict checks.
+>
+> `isNub` detects [Nub](https://github.com/nubjs/nub), which augments Node.js rather than replacing it. It is additive: `isNode` is also `true` and `runtime` stays `"node"`.
 
 See [./src/runtimes.ts](./src/runtimes.ts) for the full list.
 
diff --git a/src/index.ts b/src/index.ts
index 4bc2e48..7f2a5ba 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -41,6 +41,7 @@ export {
   isBun,
   isDeno,
   isNode,
+  isNub,
   runtime,
   runtimeInfo,
   isEdgeLight,
diff --git a/src/runtimes.ts b/src/runtimes.ts
index f57148d..14b512f 100644
--- a/src/runtimes.ts
+++ b/src/runtimes.ts
@@ -31,6 +31,15 @@ export type RuntimeInfo = {
  */
 export const isNode: boolean = !!process?.versions?.node;
 
+/**
+ * Indicates if running under [Nub](https://github.com/nubjs/nub).
+ *
+ * **Note:** Nub augments Node.js rather than replacing it, so `isNode` is also `true` and
+ * `runtime` stays `"node"`. This flag is additive — it detects the Nub augmentation layer
+ * on top of Node.
+ */
+export const isNub: boolean = !!process?.versions?.nub;
+
 /**
  * Indicates if running in Bun runtime.
  */
diff --git a/test/index.test.ts b/test/index.test.ts
index ff7e411..49b5277 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -14,6 +14,7 @@ describe("std-env", () => {
       isProduction: false,
       isDevelopment: false,
       isMinimal: true,
+      isNub: false,
       isWindows: expect.any(Boolean),
       isLinux: expect.any(Boolean),
       isMacOS: expect.any(Boolean),