diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index e69043f..1a89b27 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -43,6 +43,8 @@ jobs:
         run: |
           cd backend
           cargo test --verbose
+          cd sync_lib
+          wasm-pack test --node
 
       - name: Lint frontend
         run: |
diff --git a/backend/Cargo.lock b/backend/Cargo.lock
index 78b2aa6..dbeff8b 100644
--- a/backend/Cargo.lock
+++ b/backend/Cargo.lock
@@ -2102,6 +2102,7 @@ dependencies = [
  "base64 0.22.1",
  "console_error_panic_hook",
  "getrandom",
+ "insta",
  "reconcile",
  "thiserror",
  "wasm-bindgen",
diff --git a/backend/sync_lib/Cargo.toml b/backend/sync_lib/Cargo.toml
index 11c1f5c..864443f 100644
--- a/backend/sync_lib/Cargo.toml
+++ b/backend/sync_lib/Cargo.toml
@@ -22,6 +22,7 @@ console_error_panic_hook = { version = "0.1.7", optional = true }
 
 [dev-dependencies]
 wasm-bindgen-test = "0.3.34"
+insta = "1.41.1"
 
 [features]
 default = ["console_error_panic_hook"]
diff --git a/backend/sync_lib/src/errors.rs b/backend/sync_lib/src/errors.rs
index 68bc71c..c09eafb 100644
--- a/backend/sync_lib/src/errors.rs
+++ b/backend/sync_lib/src/errors.rs
@@ -1,5 +1,3 @@
-use std::str::Utf8Error;
-
 use base64::DecodeError;
 use thiserror::Error;
 use wasm_bindgen::JsValue;
@@ -8,9 +6,6 @@ use wasm_bindgen::JsValue;
 pub enum SyncLibError {
     #[error("Base64 decoding error because of {}", .reason)]
     Base64DecodingError { reason: String },
-
-    #[error("Bytes cannot be decoded as UTF-8 string because of {}", .reason)]
-    StringDecodingError { reason: String },
 }
 
 impl From<DecodeError> for SyncLibError {
@@ -21,14 +16,6 @@ impl From<DecodeError> for SyncLibError {
     }
 }
 
-impl From<Utf8Error> for SyncLibError {
-    fn from(e: Utf8Error) -> Self {
-        SyncLibError::StringDecodingError {
-            reason: e.to_string(),
-        }
-    }
-}
-
 impl From<std::string::FromUtf8Error> for SyncLibError {
     fn from(e: std::string::FromUtf8Error) -> Self {
         SyncLibError::Base64DecodingError {
diff --git a/backend/sync_lib/src/lib.rs b/backend/sync_lib/src/lib.rs
index 9832c5b..2258dee 100644
--- a/backend/sync_lib/src/lib.rs
+++ b/backend/sync_lib/src/lib.rs
@@ -6,53 +6,57 @@ use wasm_bindgen::prelude::*;
 
 pub mod errors;
 
+/// Encode binary data for easy transport over HTTP. Inverse of
+/// `base64_to_bytes`.
 #[wasm_bindgen(js_name = bytesToBase64)]
 pub fn bytes_to_base64(input: &[u8]) -> String { STANDARD_NO_PAD.encode(input) }
 
-#[wasm_bindgen(js_name = stringToBase64)]
-pub fn string_to_base64(input: &str) -> String { bytes_to_base64(input.as_bytes()) }
-
+/// Inverse of `bytes_to_base64`.
 #[wasm_bindgen(js_name = base64ToBytes)]
 pub fn base64_to_bytes(input: &str) -> Result<Vec<u8>, SyncLibError> {
     STANDARD_NO_PAD.decode(input).map_err(SyncLibError::from)
 }
 
-#[wasm_bindgen(js_name = base64ToString)]
-pub fn base64_to_string(input: &str) -> Result<String, SyncLibError> {
-    let bytes = base64_to_bytes(input)?;
-    String::from_utf8(bytes).map_err(SyncLibError::from)
-}
-
+/// Merge two documents with a common parent. Relies on `reconcile::reconcile`
+/// for texts and returns the right document as-is if either of the updated
+/// documents is binary.
 #[wasm_bindgen]
-pub fn merge(parent: &[u8], left: &[u8], right: &[u8]) -> Result<Vec<u8>, SyncLibError> {
-    Ok(if is_binary(right) {
+pub fn merge(parent: &[u8], left: &[u8], right: &[u8]) -> Vec<u8> {
+    if is_binary(parent) || is_binary(left) || is_binary(right) {
         right.to_vec()
     } else {
         reconcile::reconcile(
-            str::from_utf8(parent).map_err(SyncLibError::from)?,
-            str::from_utf8(left).map_err(SyncLibError::from)?,
-            str::from_utf8(right).map_err(SyncLibError::from)?,
+            str::from_utf8(parent).expect("parent must be valid UTF-8 because it's not binary"),
+            str::from_utf8(left).expect("left must be valid UTF-8 because it's not binary"),
+            str::from_utf8(right).expect("right must be valid UTF-8 because it's not binary"),
         )
         .into_bytes()
-    })
+    }
 }
 
+/// WASM wrapper around `reconcile::reconcile` for text merging.
 #[wasm_bindgen(js_name = mergeText)]
 pub fn merge_text(parent: &str, left: &str, right: &str) -> String {
     reconcile::reconcile(parent, left, right)
 }
 
+/// Heuristically determine if the given data is a binary or a text file's
+/// content.
 #[wasm_bindgen(js_name = isBinary)]
-pub fn is_binary(data: &[u8]) -> bool { std::str::from_utf8(data).is_ok() }
+pub fn is_binary(data: &[u8]) -> bool {
+    if data.iter().any(|&b| b == 0) {
+        // Even though the NUL character is valid in UTF-8, it's highly suspicious in
+        // human-readable text.
+        return true;
+    }
 
+    std::str::from_utf8(data).is_err()
+}
+
+/// Set up panic hook for better error messages in the browser console.
 #[cfg(feature = "console_error_panic_hook")]
 #[wasm_bindgen(js_name = setPanicHook)]
 pub fn set_panic_hook() {
-    // When the `console_error_panic_hook` feature is enabled, we can call the
-    // `set_panic_hook` function at least once during initialization, and then
-    // we will get better error messages if our code ever panics.
-    //
-    // For more details see
     // https://github.com/rustwasm/console_error_panic_hook#readme
     console_error_panic_hook::set_once();
 }
diff --git a/backend/sync_lib/tests/snapshots/web__base64_to_bytes_error.snap b/backend/sync_lib/tests/snapshots/web__base64_to_bytes_error.snap
new file mode 100644
index 0000000..fa17876
--- /dev/null
+++ b/backend/sync_lib/tests/snapshots/web__base64_to_bytes_error.snap
@@ -0,0 +1,10 @@
+---
+source: sync_lib/tests/web.rs
+expression: base64_to_bytes(input)
+snapshot_kind: text
+---
+Err(
+    Base64DecodingError {
+        reason: "Invalid symbol 61, offset 0.",
+    },
+)
diff --git a/backend/sync_lib/tests/web.rs b/backend/sync_lib/tests/web.rs
index de5c1da..642ceaa 100644
--- a/backend/sync_lib/tests/web.rs
+++ b/backend/sync_lib/tests/web.rs
@@ -1,13 +1,46 @@
 //! Test suite for the Web and headless browsers.
 
-#![cfg(target_arch = "wasm32")]
-
-extern crate wasm_bindgen_test;
+use insta::assert_debug_snapshot;
+use sync_lib::*;
 use wasm_bindgen_test::*;
 
-wasm_bindgen_test_configure!(run_in_browser);
-
-#[wasm_bindgen_test]
-fn pass() {
-    assert_eq!(1 + 1, 2);
+#[wasm_bindgen_test(unsupported = test)]
+fn test_bytes_to_base64() {
+    let input = b"hello";
+    let expected = "aGVsbG8";
+    assert_eq!(bytes_to_base64(input), expected);
+}
+
+#[wasm_bindgen_test(unsupported = test)]
+fn test_base64_to_bytes() {
+    let input = "aGVsbG8";
+    let expected = b"hello".to_vec();
+    assert_eq!(base64_to_bytes(input).unwrap(), expected);
+}
+
+#[test] // insta doesn't support wasm-bindgen-test
+fn test_base64_to_bytes_error() {
+    let input = "===";
+    assert_debug_snapshot!(base64_to_bytes(input));
+}
+
+#[wasm_bindgen_test(unsupported = test)]
+fn merge_text() {
+    let left = b"hello ";
+    let right = b"world";
+    assert_eq!(merge(b"", left, right), b"hello world".to_vec());
+}
+
+#[wasm_bindgen_test(unsupported = test)]
+fn merge_binary() {
+    let left = [0, 1, 2];
+    let right = [3, 4, 5];
+    assert_eq!(merge(b"", &left, &right), right);
+}
+
+#[wasm_bindgen_test(unsupported = test)]
+fn test_is_binary() {
+    assert!(is_binary(&[0, 159, 146, 150]));
+    assert!(is_binary(&[0, 12]));
+    assert!(!is_binary(b"hello"));
 }