diff --git a/wasm/.cargo/config.toml b/wasm/.cargo/config.toml
index f5d9120..461a6af 100644
--- a/wasm/.cargo/config.toml
+++ b/wasm/.cargo/config.toml
@@ -1,2 +1,5 @@
+[build]
+target = "wasm32-unknown-unknown"
+
 [target.wasm32-unknown-unknown]
 rustflags = ["--cfg=web_sys_unstable_apis"]
diff --git a/wasm/Cargo.toml b/wasm/Cargo.toml
index f83278c..3ac76f7 100644
--- a/wasm/Cargo.toml
+++ b/wasm/Cargo.toml
@@ -38,3 +38,7 @@ mtp-common = { path = "../common" }
 mtp-type-map = { path = "../type-map" }
 mtp-codec = { path = "../codec", features = ["crypto"] }
 mtp-crypto = { path = "../crypto", features = ["wasm"] }
+
+[dev-dependencies]
+wasm-bindgen-test = "0.3"
+hex = "0.4"
diff --git a/wasm/src/crypto.rs b/wasm/src/crypto.rs
index 21f4082..401fabe 100644
--- a/wasm/src/crypto.rs
+++ b/wasm/src/crypto.rs
@@ -261,3 +261,218 @@ pub fn wasm_derive_encryption_key(
         .map(|key| key.to_vec())
         .map_err(|e| js_error(&format!("derive_encryption_key failed: {}", e)))
 }
+
+#[cfg(test)]
+#[cfg(target_arch = "wasm32")]
+mod tests {
+    use super::*;
+    use wasm_bindgen_test::*;
+
+    // ------------------------------------------------------------------
+    // Keyring
+    // ------------------------------------------------------------------
+
+    #[wasm_bindgen_test]
+    fn keyring_from_ed25519_roundtrip() {
+        let sk = vec![0xabu8; 32];
+        let pk = vec![0x42u8; 32];
+        let bytes = keyring_from_ed25519(&sk, &pk).expect("keyring_from_ed25519 failed");
+
+        let restored = WasmKeyring::from_bytes(&bytes).expect("from_bytes failed");
+        let bundle = restored.public_key_bundle();
+        assert_eq!(bundle.sig_cl_public_key(), pk);
+    }
+
+    #[wasm_bindgen_test]
+    fn keyring_from_ed25519_wrong_key_length() {
+        let short = vec![0u8; 16];
+        let ok = vec![0u8; 32];
+        assert!(keyring_from_ed25519(&short, &ok).is_err());
+        assert!(keyring_from_ed25519(&ok, &short).is_err());
+    }
+
+    // ------------------------------------------------------------------
+    // PublicKeyBundle
+    // ------------------------------------------------------------------
+
+    #[wasm_bindgen_test]
+    fn public_key_bundle_roundtrip() {
+        let pk = vec![0x99u8; 32];
+        let bundle = WasmPublicKeyBundle {
+            inner: PublicKeyBundle {
+                kem_public_key: KemPublicKey::new(vec![1, 2, 3]),
+                sig_cl_public_key: SignaturePublicKey::new(pk.clone()),
+                sig_pq_public_key: SignaturePqPublicKey::new(vec![4, 5, 6]),
+            },
+        };
+
+        let bytes = bundle.to_bytes();
+        let restored = WasmPublicKeyBundle::from_bytes(&bytes).expect("from_bytes failed");
+        assert_eq!(restored.sig_cl_public_key(), pk);
+    }
+
+    // ------------------------------------------------------------------
+    // ChaCha20-Poly1305
+    // ------------------------------------------------------------------
+
+    #[wasm_bindgen_test]
+    fn chacha20_encrypt_decrypt_roundtrip() {
+        let key = vec![0x42u8; 32];
+        let cipher = WasmChaCha20Poly1305::new(key).expect("new failed");
+
+        let plaintext = b"hello wasm crypto";
+        let aad = b"test-aad";
+
+        let encrypted = cipher.encrypt(plaintext, aad).expect("encrypt failed");
+        let decrypted = cipher.decrypt(&encrypted, aad).expect("decrypt failed");
+
+        assert_eq!(decrypted, plaintext);
+    }
+
+    #[wasm_bindgen_test]
+    fn chacha20_wrong_key_length() {
+        assert!(WasmChaCha20Poly1305::new(vec![0u8; 16]).is_err());
+        assert!(WasmChaCha20Poly1305::new(vec![0u8; 31]).is_err());
+        assert!(WasmChaCha20Poly1305::new(vec![0u8; 33]).is_err());
+    }
+
+    #[wasm_bindgen_test]
+    fn chacha20_decrypt_wrong_key_fails() {
+        let key1 = vec![0x42u8; 32];
+        let key2 = vec![0x43u8; 32];
+        let cipher1 = WasmChaCha20Poly1305::new(key1).expect("new failed");
+        let cipher2 = WasmChaCha20Poly1305::new(key2).expect("new failed");
+
+        let encrypted = cipher1.encrypt(b"secret", b"aad").expect("encrypt failed");
+        let result = cipher2.decrypt(&encrypted, b"aad");
+        assert!(result.is_err());
+    }
+
+    // ------------------------------------------------------------------
+    // Ed25519
+    // ------------------------------------------------------------------
+
+    #[wasm_bindgen_test]
+    fn ed25519_sign_verify() {
+        let (_signer, sk, _pk) = Ed25519Signer::generate();
+
+        let signer = WasmEd25519Signer::new(sk.as_bytes().to_vec()).expect("new failed");
+        let message = b"test message for ed25519";
+
+        let signature = signer.sign(message).expect("sign failed");
+        assert!(!signature.is_empty());
+
+        signer.verify(message, &signature).expect("verify failed");
+    }
+
+    #[wasm_bindgen_test]
+    fn ed25519_sign_wrong_message_fails_verify() {
+        let (_signer, sk, _pk) = Ed25519Signer::generate();
+
+        let signer = WasmEd25519Signer::new(sk.as_bytes().to_vec()).expect("new failed");
+        let signature = signer.sign(b"message A").expect("sign failed");
+
+        let result = signer.verify(b"message B", &signature);
+        assert!(result.is_err());
+    }
+
+    #[wasm_bindgen_test]
+    fn ed25519_generate_returns_valid() {
+        let result = ed25519_generate().expect("generate failed");
+
+        let has_signer = js_sys::Reflect::has(&result, &"signer".into()).unwrap_or(false);
+        let has_sk = js_sys::Reflect::has(&result, &"secretKey".into()).unwrap_or(false);
+        let has_pk = js_sys::Reflect::has(&result, &"publicKey".into()).unwrap_or(false);
+
+        assert!(has_signer);
+        assert!(has_sk);
+        assert!(has_pk);
+    }
+
+    #[wasm_bindgen_test]
+    fn ed25519_verify_standalone() {
+        let (_signer, sk, pk) = Ed25519Signer::generate();
+        let signer = WasmEd25519Signer::new(sk.as_bytes().to_vec()).expect("new failed");
+        let msg = b"standalone verify test";
+        let sig = signer.sign(msg).expect("sign failed");
+
+        ed25519_verify(pk.as_bytes().to_vec(), msg, &sig).expect("verify failed");
+    }
+
+    #[wasm_bindgen_test]
+    fn ed25519_verify_bad_signature_fails() {
+        let pk = vec![0x42u8; 32];
+        let msg = b"test";
+        let bad_sig = vec![0x00u8; 64];
+        let result = ed25519_verify(pk, msg, &bad_sig);
+        assert!(result.is_err());
+    }
+
+    // ------------------------------------------------------------------
+    // Hashing
+    // ------------------------------------------------------------------
+
+    #[wasm_bindgen_test]
+    fn sha256_empty() {
+        let result = wasm_sha256(b"");
+        // SHA-256 of empty string
+        let expected = hex::decode("e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855")
+            .expect("hex decode");
+        assert_eq!(result, expected);
+    }
+
+    #[wasm_bindgen_test]
+    fn sha256_hello() {
+        let result = wasm_sha256(b"hello");
+        let expected = hex::decode("2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824")
+            .expect("hex decode");
+        assert_eq!(result, expected);
+    }
+
+    #[wasm_bindgen_test]
+    fn sha256_double() {
+        let single = wasm_sha256(b"test");
+        let double = wasm_sha256_double(b"test");
+        let expected = wasm_sha256(&single);
+        assert_eq!(double, expected);
+    }
+
+    // ------------------------------------------------------------------
+    // HKDF / KDF
+    // ------------------------------------------------------------------
+
+    #[wasm_bindgen_test]
+    fn hkdf_expand_produces_correct_length() {
+        let result = wasm_hkdf_expand(b"ikm", b"salt", b"info", 32)
+            .expect("hkdf_expand failed");
+        assert_eq!(result.len(), 32);
+    }
+
+    #[wasm_bindgen_test]
+    fn hkdf_expand_different_info() {
+        let r1 = wasm_hkdf_expand(b"ikm", b"salt", b"info1", 16).expect("hkdf failed");
+        let r2 = wasm_hkdf_expand(b"ikm", b"salt", b"info2", 16).expect("hkdf failed");
+        assert_ne!(r1, r2);
+    }
+
+    #[wasm_bindgen_test]
+    fn derive_encryption_key_roundtrip() {
+        let key = wasm_derive_encryption_key(b"password", b"salt", b"context")
+            .expect("derive failed");
+        assert_eq!(key.len(), 32);
+
+        // Deterministic: same inputs = same key
+        let key2 = wasm_derive_encryption_key(b"password", b"salt", b"context")
+            .expect("derive failed");
+        assert_eq!(key, key2);
+    }
+
+    #[wasm_bindgen_test]
+    fn derive_encryption_key_different_inputs_different_key() {
+        let key = wasm_derive_encryption_key(b"pass1", b"salt", b"context")
+            .expect("derive failed");
+        let key2 = wasm_derive_encryption_key(b"pass2", b"salt", b"context")
+            .expect("derive failed");
+        assert_ne!(key, key2);
+    }
+}
diff --git a/wasm/src/error.rs b/wasm/src/error.rs
index c4dc93f..c3ed596 100644
--- a/wasm/src/error.rs
+++ b/wasm/src/error.rs
@@ -15,3 +15,48 @@ pub fn from_communication_error(e: mtp_common::CommunicationError) -> JsValue {
 pub fn from_crypto_error(e: mtp_crypto::CryptoError) -> JsValue {
     js_error(e.to_string())
 }
+
+#[cfg(test)]
+#[cfg(target_arch = "wasm32")]
+mod tests {
+    use super::*;
+    use wasm_bindgen_test::*;
+
+    #[wasm_bindgen_test]
+    fn js_error_contains_message() {
+        let err = js_error("test error message");
+        assert_eq!(err.as_string(), Some("test error message".to_string()));
+    }
+
+    #[wasm_bindgen_test]
+    fn js_error_from_string() {
+        let err = js_error(String::from("owned string error"));
+        assert_eq!(err.as_string(), Some("owned string error".to_string()));
+    }
+
+    #[wasm_bindgen_test]
+    fn from_codec_error_invalid_encoding() {
+        let err = from_codec_error(mtp_common::CodecError::InvalidEncoding);
+        assert!(err.as_string().unwrap().contains("Invalid encoding"));
+    }
+
+    #[wasm_bindgen_test]
+    fn from_codec_error_unknown_version() {
+        let err = from_codec_error(mtp_common::CodecError::UnknownVersion);
+        assert!(err.as_string().unwrap().contains("Unknown version"));
+    }
+
+    #[wasm_bindgen_test]
+    fn from_communication_error_renders() {
+        use mtp_common::CommunicationError;
+        let err = from_communication_error(CommunicationError::ConnectionLost);
+        assert!(err.as_string().unwrap().contains("Connection terminated"));
+    }
+
+    #[wasm_bindgen_test]
+    fn from_crypto_error_renders() {
+        use mtp_crypto::CryptoError;
+        let err = from_crypto_error(CryptoError::InvalidKeyLength);
+        assert!(err.as_string().unwrap().contains("invalid key length"));
+    }
+}
diff --git a/wasm/src/lib.rs b/wasm/src/lib.rs
index bb4ef3d..183730d 100644
--- a/wasm/src/lib.rs
+++ b/wasm/src/lib.rs
@@ -1,11 +1,12 @@
-pub mod error;
-pub mod transport;
 pub mod client;
 pub mod crypto;
+pub mod error;
 pub mod message;
+pub mod transport;
 
 use wasm_bindgen::prelude::*;
 
+#[cfg(not(test))]
 #[wasm_bindgen(start)]
 pub fn main() {
     console_error_panic_hook::set_once();
diff --git a/wasm/src/message.rs b/wasm/src/message.rs
index 0d17646..0212cd9 100644
--- a/wasm/src/message.rs
+++ b/wasm/src/message.rs
@@ -1,7 +1,7 @@
 use wasm_bindgen::prelude::*;
 
 use mtp_codec::{
-    CommunicationType, CommunicationValue, DataType, DataTypeId, DataValue,
+    CommunicationType, CommunicationTypeId, CommunicationValue, DataType, DataTypeId, DataValue,
 };
 use mtp_crypto::{
     ChaCha20Poly1305, Ed25519Signer, Keyring, SigAlgorithm,
@@ -133,3 +133,130 @@ pub fn parse_auth_response(response: &[u8]) -> Result<JsValue, JsValue> {
 
     Ok(obj.into())
 }
+
+#[cfg(test)]
+#[cfg(target_arch = "wasm32")]
+mod tests {
+    use super::*;
+    use wasm_bindgen_test::*;
+
+    #[wasm_bindgen_test]
+    fn build_ping_frame_roundtrip() {
+        let bytes = build_ping_frame(42, "test-ping", 1234567890, &[]);
+        let cv = CommunicationValue::from_bytes(&bytes).expect("decode failed");
+
+        assert_eq!(cv.get_type(), CommunicationTypeId(19)); // Ping
+        assert_eq!(cv.get_sender(), 42);
+        assert_eq!(cv.get_data(DataTypeId(4)), &DataValue::Str("test-ping".into()));
+        assert_eq!(cv.get_data(DataTypeId(5)), &DataValue::UnsignedNumber(1234567890));
+    }
+
+    #[wasm_bindgen_test]
+    fn build_ping_frame_with_data() {
+        let payload = b"attachment-data";
+        let bytes = build_ping_frame(99, "with-data", 555, payload);
+        let cv = CommunicationValue::from_bytes(&bytes).expect("decode failed");
+
+        assert_eq!(cv.get_type(), CommunicationTypeId(19));
+        assert_eq!(cv.get_sender(), 99);
+        assert_eq!(cv.get_data(DataTypeId(4)), &DataValue::Str("with-data".into()));
+        assert_eq!(cv.get_data(DataTypeId(5)), &DataValue::UnsignedNumber(555));
+        assert_eq!(cv.get_data(DataTypeId(6)), &DataValue::Bytes(payload.to_vec()));
+    }
+
+    #[wasm_bindgen_test]
+    fn build_ping_frame_client_id_zero() {
+        let bytes = build_ping_frame(0, "zero-id", 0, &[]);
+        let cv = CommunicationValue::from_bytes(&bytes).expect("decode failed");
+        assert_eq!(cv.get_sender(), 0);
+    }
+
+    #[wasm_bindgen_test]
+    fn build_demo_message_roundtrip() {
+        let (_signer, sk, pk) = Ed25519Signer::generate();
+        let keyring = Keyring::new(
+            mtp_crypto::KemPublicKey::new(vec![]),
+            mtp_crypto::KemPrivateKey::new(vec![]),
+            mtp_crypto::SignaturePqPublicKey::new(vec![]),
+            mtp_crypto::SignaturePqPrivateKey::new(vec![]),
+            pk,
+            sk,
+        );
+        let keyring_bytes = keyring.to_bytes();
+
+        let result = build_demo_message(7, &keyring_bytes);
+        assert!(result.is_ok());
+
+        let bytes = result.unwrap();
+        let cv = CommunicationValue::from_bytes(&bytes).expect("decode failed");
+
+        assert_eq!(cv.get_type(), CommunicationTypeId(19)); // Ping
+        assert_eq!(cv.get_sender(), 7);
+        assert_eq!(cv.get_data(DataTypeId(4)), &DataValue::Str("MTP WASM Demo".into()));
+    }
+
+    #[wasm_bindgen_test]
+    fn build_demo_message_invalid_keyring() {
+        let result = build_demo_message(1, b"not-a-valid-keyring");
+        assert!(result.is_err());
+        let err = result.unwrap_err();
+        assert!(err.as_string().unwrap().contains("invalid keyring"));
+    }
+
+    #[wasm_bindgen_test]
+    fn parse_auth_response_success() {
+        let resp = CommunicationValue::new(CommunicationType::IdentificationResponse)
+            .add_typed_default(DataType::Connected, DataValue::BoolTrue)
+            .add_typed_default(DataType::ClientNonce, DataValue::UnsignedNumber(999))
+            .add_typed_default(DataType::Id, DataValue::UnsignedNumber(42))
+            .add_typed_default(DataType::Timestamp, DataValue::UnsignedNumber(12345))
+            .to_bytes();
+
+        let result = parse_auth_response(&resp).expect("parse failed");
+
+        let connected = js_sys::Reflect::get(&result, &"connected".into())
+            .ok().and_then(|v| v.as_bool());
+        assert_eq!(connected, Some(true));
+
+        let id = js_sys::Reflect::get(&result, &"assignedId".into())
+            .ok().and_then(|v| v.as_f64());
+        assert_eq!(id, Some(42.0));
+    }
+
+    #[wasm_bindgen_test]
+    fn parse_auth_response_rejected() {
+        let resp = CommunicationValue::new(CommunicationType::IdentificationResponse)
+            .add_typed_default(DataType::Connected, DataValue::BoolFalse)
+            .to_bytes();
+
+        let result = parse_auth_response(&resp).expect("parse failed");
+
+        let connected = js_sys::Reflect::get(&result, &"connected".into())
+            .ok().and_then(|v| v.as_bool());
+        assert_eq!(connected, Some(false));
+
+        // rejected should have no assignedId
+        let has_id = js_sys::Reflect::has(&result, &"assignedId".into()).unwrap_or(false);
+        assert!(!has_id);
+    }
+
+    #[wasm_bindgen_test]
+    fn parse_auth_response_with_signature() {
+        let sig_bytes = vec![0xde, 0xad, 0xbe, 0xef, 0xca, 0xfe];
+        let resp = CommunicationValue::new(CommunicationType::IdentificationResponse)
+            .add_typed_default(DataType::Connected, DataValue::BoolTrue)
+            .add_typed_default(DataType::Signature, DataValue::Bytes(sig_bytes.clone()))
+            .to_bytes();
+
+        let result = parse_auth_response(&resp).expect("parse failed");
+
+        let has_sig = js_sys::Reflect::has(&result, &"signature".into()).unwrap_or(false);
+        assert!(has_sig);
+    }
+
+    #[wasm_bindgen_test]
+    fn parse_auth_response_invalid_frame() {
+        let result = parse_auth_response(b"garbage-data");
+        assert!(result.is_err());
+    }
+}