diff --git a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
index e8169644085..3947995b2fe 100644
--- a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
+++ b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.cpp
@@ -1757,6 +1757,18 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<JS::ArrayBuffer>> AesCtr::decrypt(Algorithm
     return JS::ArrayBuffer::create(m_realm, plaintext);
 }
 
+WebIDL::ExceptionOr<JS::Value> AesGcm::get_key_length(AlgorithmParams const& params)
+{
+    // 1. If the length member of normalizedDerivedKeyAlgorithm is not 128, 192 or 256, then throw a OperationError.
+    auto const& normalized_algorithm = static_cast<AesDerivedKeyParams const&>(params);
+    auto length = normalized_algorithm.length;
+    if (length != 128 && length != 192 && length != 256)
+        return WebIDL::OperationError::create(m_realm, "Invalid key length"_string);
+
+    // 2. Return the length member of normalizedDerivedKeyAlgorithm.
+    return JS::Value(length);
+}
+
 // https://w3c.github.io/webcrypto/#hkdf-operations
 WebIDL::ExceptionOr<JS::NonnullGCPtr<CryptoKey>> HKDF::import_key(AlgorithmParams const&, Bindings::KeyFormat format, CryptoKey::InternalKeyData key_data, bool extractable, Vector<Bindings::KeyUsage> const& key_usages)
 {
diff --git a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
index 1722adf4b2c..8ee818eda3b 100644
--- a/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
+++ b/Userland/Libraries/LibWeb/Crypto/CryptoAlgorithms.h
@@ -362,6 +362,19 @@ private:
     }
 };
 
+class AesGcm : public AlgorithmMethods {
+public:
+    virtual WebIDL::ExceptionOr<JS::Value> get_key_length(AlgorithmParams const&) override;
+
+    static NonnullOwnPtr<AlgorithmMethods> create(JS::Realm& realm) { return adopt_own(*new AesGcm(realm)); }
+
+private:
+    explicit AesGcm(JS::Realm& realm)
+        : AlgorithmMethods(realm)
+    {
+    }
+};
+
 class HKDF : public AlgorithmMethods {
 public:
     virtual WebIDL::ExceptionOr<JS::NonnullGCPtr<CryptoKey>> import_key(AlgorithmParams const&, Bindings::KeyFormat, CryptoKey::InternalKeyData, bool, Vector<Bindings::KeyUsage> const&) override;
diff --git a/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp b/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
index 0c08e0d7b96..9c7ac62dd22 100644
--- a/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
+++ b/Userland/Libraries/LibWeb/Crypto/SubtleCrypto.cpp
@@ -784,6 +784,9 @@ SupportedAlgorithmsMap supported_algorithms()
     define_an_algorithm<AesCtr, AesDerivedKeyParams>("get key length"_string, "AES-CTR"_string);
     define_an_algorithm<AesCtr, AesKeyGenParams>("generateKey"_string, "AES-CTR"_string);
 
+    // https://w3c.github.io/webcrypto/#aes-gcm-registration
+    define_an_algorithm<AesGcm, AesDerivedKeyParams>("get key length"_string, "AES-GCM"_string);
+
     // https://w3c.github.io/webcrypto/#hkdf
     define_an_algorithm<HKDF>("importKey"_string, "HKDF"_string);
     define_an_algorithm<HKDF, HKDFParams>("deriveBits"_string, "HKDF"_string);