diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 35ae9828..2de7e81d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -70,13 +70,53 @@ jobs:
             test-results
           if-no-files-found: ignore
 
-      - name: Run unit tests
-        run: npm run test:unit
-
       - name: Fail if visual regressions detected
         if: steps.visual.outcome == 'failure'
         run: exit 1
 
+  unit-tests:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        node-version: [20]
+        shard: [1, 2, 3]
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+
+      - name: Cache npm directory
+        uses: actions/cache@v4
+        with:
+          path: ~/.npm
+          key: ${{ runner.os }}-node-${{ matrix.node-version }}-npm-${{ hashFiles('package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-node-${{ matrix.node-version }}-npm-
+
+      - name: Cache node_modules
+        id: node-modules-cache
+        uses: actions/cache@v4
+        with:
+          path: node_modules
+          key: ${{ runner.os }}-node-${{ matrix.node-version }}-modules-${{ hashFiles('package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-node-${{ matrix.node-version }}-modules-
+
+      - name: Install dependencies
+        if: steps.node-modules-cache.outputs.cache-hit != 'true'
+        run: npm ci
+
+      - name: Run unit tests (shard ${{ matrix.shard }}/3)
+        env:
+          UNIT_TEST_TIMEOUT_MS: 300000
+        run: npm run test:unit:shard${{ matrix.shard }}
+
   dm-unit-tests:
     runs-on: ubuntu-latest
     strategy:
diff --git a/README.md b/README.md
index 9ca262ff..32fd8737 100644
--- a/README.md
+++ b/README.md
@@ -387,7 +387,7 @@ placeholder at “—” and development builds log a warning—so mixed deploym
 4. **Make Changes**:
    - Ensure your code follows best practices and is well-documented.
 5. **Test**:
-   - Run unit tests: `npm run test:unit`
+   - Run unit tests: `npm run test:unit` (or a shard like `npm run test:unit:shard1`)
    - Validate the site functionality locally before submitting.
 6. **Submit a Pull Request**:
    - Explain your changes and reference any related issues.
@@ -405,8 +405,12 @@ placeholder at “—” and development builds log a warning—so mixed deploym
 
 Continuous integration runs CSS linting/builds, the DM unit/integration suites, the Playwright kitchen-sink snapshots, headless E2E flows, and the Node-based unit tests on every push.
 Before pushing, run `npm run build` locally so the Tailwind bundle regenerates.
-Pair that with `npm run test:unit` for application logic changes and
-`npm run test:visual` for presentation updates to mirror the CI surface area.
+Pair that with `npm run test:unit` for application logic changes, or a shard
+(`npm run test:unit:shard1`, `test:unit:shard2`, `test:unit:shard3`) when you want to
+split the suite. You can also set `UNIT_TEST_SHARD=1/3` or pass `--shard=1/3`
+to `scripts/run-unit-tests.mjs` for custom shard splits, and use
+`UNIT_TEST_TIMEOUT_MS=120000` to abort a single stalled test file without
+blocking the entire run. `npm run test:visual` covers presentation updates to mirror the CI surface area.
 For DM-specific changes, also run `npm run test:dm:unit` and
 `npm run test:dm:integration` to cover the direct message flows.
 Use `npm run test:e2e` to execute the headless Playwright journeys in `tests/e2e`.
diff --git a/package.json b/package.json
index d87d02d3..ada1e56d 100644
--- a/package.json
+++ b/package.json
@@ -24,6 +24,9 @@
     "test:dm:unit": "node scripts/run-targeted-tests.mjs tests/dm-db.test.mjs tests/dm-decryptor.test.mjs tests/dm-normalization.test.mjs tests/nostr-send-direct-message.test.mjs",
     "test:dm:integration": "node scripts/run-targeted-tests.mjs tests/nostr/dm-direct-message-flow.test.mjs",
     "test:unit": "node scripts/run-unit-tests.mjs",
+    "test:unit:shard1": "cross-env UNIT_TEST_SHARD=1/3 node scripts/run-unit-tests.mjs",
+    "test:unit:shard2": "cross-env UNIT_TEST_SHARD=2/3 node scripts/run-unit-tests.mjs",
+    "test:unit:shard3": "cross-env UNIT_TEST_SHARD=3/3 node scripts/run-unit-tests.mjs",
     "telemetry:aggregate": "node scripts/telemetry-aggregator.mjs"
   },
   "devDependencies": {
diff --git a/scripts/run-unit-tests.mjs b/scripts/run-unit-tests.mjs
index e131fd94..f22ad3ae 100755
--- a/scripts/run-unit-tests.mjs
+++ b/scripts/run-unit-tests.mjs
@@ -7,6 +7,17 @@ const rootDir = path.dirname(fileURLToPath(new URL("../package.json", import.met
 const testsDir = path.join(rootDir, "tests");
 const testFiles = [];
 const setupImport = new URL("../tests/test-helpers/setup-localstorage.mjs", import.meta.url);
+const shardArg = process.argv.find((arg) => arg.startsWith("--shard="));
+const shardValue = shardArg ? shardArg.split("=")[1] : process.env.UNIT_TEST_SHARD;
+const timeoutMs = process.env.UNIT_TEST_TIMEOUT_MS
+  ? Number(process.env.UNIT_TEST_TIMEOUT_MS)
+  : null;
+
+if (timeoutMs !== null && (!Number.isFinite(timeoutMs) || timeoutMs <= 0)) {
+  throw new Error(
+    "UNIT_TEST_TIMEOUT_MS must be a positive number representing milliseconds.",
+  );
+}
 
 async function collectTests(dir) {
   const entries = await readdir(dir, { withFileTypes: true });
@@ -40,42 +51,120 @@ async function collectTests(dir) {
   }
 }
 
-await collectTests(testsDir);
+function parseShard(value) {
+  if (!value) {
+    return null;
+  }
 
-testFiles.sort((a, b) => a.localeCompare(b));
+  const match = /^(\d+)\/(\d+)$/.exec(value.trim());
+  if (!match) {
+    throw new Error("Shard format must be <index>/<total>, e.g. 1/3.");
+  }
 
-if (testFiles.length === 0) {
-  console.log("No unit tests found.");
-  process.exit(0);
+  const index = Number(match[1]);
+  const total = Number(match[2]);
+
+  if (!Number.isInteger(index) || !Number.isInteger(total) || total < 1) {
+    throw new Error("Shard values must be positive integers.");
+  }
+
+  if (index < 1 || index > total) {
+    throw new Error("Shard index must be between 1 and total (inclusive).");
+  }
+
+  return { index, total };
 }
 
-for (const testFile of testFiles) {
-  const relativePath = path.relative(rootDir, testFile);
-  console.log(`\n→ Running ${relativePath}`);
+async function run() {
+  await collectTests(testsDir);
 
-  await new Promise((resolve, reject) => {
-    const child = spawn(process.execPath, ["--import", setupImport.href, testFile], {
-      stdio: "inherit",
-    });
+  testFiles.sort((a, b) => a.localeCompare(b));
 
-    child.on("close", (code, signal) => {
-      if (signal) {
-        reject(new Error(`${relativePath} exited with signal ${signal}`));
-        return;
+  if (testFiles.length === 0) {
+    console.log("No unit tests found.");
+    return;
+  }
+
+  const shard = parseShard(shardValue);
+  const selectedTests = shard
+    ? testFiles.filter((_, index) => index % shard.total === shard.index - 1)
+    : testFiles;
+
+  if (shard) {
+    console.log(
+      `Using shard ${shard.index}/${shard.total} (${selectedTests.length} of ${testFiles.length} files).`,
+    );
+  }
+
+  if (selectedTests.length === 0) {
+    console.log("No unit tests found for this shard.");
+    return;
+  }
+
+  for (const testFile of selectedTests) {
+    const relativePath = path.relative(rootDir, testFile);
+    console.log(`\n→ Running ${relativePath}`);
+
+    await new Promise((resolve, reject) => {
+      const child = spawn(process.execPath, ["--import", setupImport.href, testFile], {
+        stdio: "inherit",
+      });
+      let finished = false;
+      let timeoutId = null;
+
+      const finalize = (error) => {
+        if (finished) {
+          return;
+        }
+        finished = true;
+
+        if (timeoutId) {
+          clearTimeout(timeoutId);
+        }
+
+        if (error) {
+          reject(error);
+          return;
+        }
+
+        resolve();
+      };
+
+      if (timeoutMs !== null) {
+        timeoutId = setTimeout(() => {
+          child.kill("SIGKILL");
+          finalize(
+            new Error(`${relativePath} timed out after ${timeoutMs}ms and was aborted.`),
+          );
+        }, timeoutMs);
       }
 
-      if (code !== 0) {
-        reject(new Error(`${relativePath} failed with exit code ${code}`));
-        return;
-      }
+      child.on("close", (code, signal) => {
+        if (signal) {
+          finalize(new Error(`${relativePath} exited with signal ${signal}`));
+          return;
+        }
 
-      resolve();
-    });
+        if (code !== 0) {
+          finalize(new Error(`${relativePath} failed with exit code ${code}`));
+          return;
+        }
 
-    child.on("error", (error) => {
-      reject(error);
+        finalize();
+      });
+
+      child.on("error", (error) => {
+        finalize(error);
+      });
     });
-  });
+  }
+
+  console.log("\n✔ All unit tests passed");
 }
 
-console.log("\n✔ All unit tests passed");
+try {
+  await run();
+} catch (error) {
+  console.error(`\n✖ ${error.message}`);
+  process.exit(1);
+}