Feat: File Integrity Checker

README.md

@@ -56,6 +56,7 @@ Here is the list of all utilities:
 - [Random String Generator](https://jam.dev/utilities/random-string-generator)
 - [CSV file viewer](https://jam.dev/utilities/csv-file-viewer)
 - [JSONL Validator](https://jam.dev/utilities/jsonl-validator)
+- [File Integrity Checker](https://jam.dev/utilities/file-integrity-checker)
 
 ### Built With
 

__tests__/pages/utilities/file-integrity-checker.test.tsx

@@ -0,0 +1,38 @@
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import FileIntegrityChecker from "../../../pages/utilities/file-integrity-checker";
+
+describe("FileIntegrityChecker", () => {
+  test("computes the sha256 hash automatically as soon as a file is uploaded", async () => {
+    render(<FileIntegrityChecker />);
+
+    const user = userEvent.setup();
+    const file = new File(["hello world"], "hello.txt", {
+      type: "text/plain",
+    });
+
+    await user.upload(screen.getByTestId("input"), file);
+
+    expect(await screen.findByText(/sha-256 hash/i)).toBeInTheDocument();
+    expect(screen.getByDisplayValue(/^[a-f0-9]{64}$/i)).toBeInTheDocument();
+  });
+
+  test("switching algorithms clears the stale hash and recomputes for the new one", async () => {
+    render(<FileIntegrityChecker />);
+
+    const user = userEvent.setup();
+    const file = new File(["hello world"], "hello.txt", {
+      type: "text/plain",
+    });
+
+    await user.upload(screen.getByTestId("input"), file);
+    await screen.findByDisplayValue(/^[a-f0-9]{64}$/i); // sha256 by default
+
+    await user.selectOptions(screen.getByLabelText(/hash algorithm/i), "md5");
+
+    expect(await screen.findByText(/md5 hash/i)).toBeInTheDocument();
+    expect(
+      await screen.findByDisplayValue(/^[a-f0-9]{32}$/i)
+    ).toBeInTheDocument();
+  });
+});

components/seo/FileIntegrityCheckerSEO.tsx

@@ -0,0 +1,101 @@
+export default function FileIntegrityCheckerSEO() {
+  return (
+    <div className="content-wrapper">
+      <section>
+        <p>
+          Generate a checksum (hash) of any file to confirm it wasn&apos;t
+          corrupted during download or transfer, or tampered with along the way.
+          If the hash you calculate matches the hash published by the
+          file&apos;s source, the file is identical, byte for byte, to the
+          original.
+        </p>
+      </section>
+
+      <section>
+        <p>
+          Drop a file into the tool above or click to browse for one. Large
+          files are streamed in chunks, so there&apos;s no file size limit and
+          nothing is ever uploaded anywhere.
+        </p>
+      </section>
+
+      <section>
+        <h2>How to Check File Integrity</h2>
+        <ul>
+          <li>
+            <b>Drop in or browse for your file:</b> <br /> Drag and drop the
+            file directly or click to select it from your machine.
+          </li>
+          <li>
+            <b>Pick the algorithm:</b> <br /> Choose SHA-256, SHA-512, or MD5 to
+            match the hash you were given.
+          </li>
+          <li>
+            <b>Wait for the hash to generate:</b> <br /> Large files are
+            streamed in chunks, so even multi-gigabyte files can be checked
+            without running out of memory.
+          </li>
+          <li>
+            <b>Verify against a known hash:</b> <br /> Paste the published hash
+            into the verify field to confirm it matches.
+          </li>
+        </ul>
+      </section>
+
+      <section>
+        <h2>SHA-256 vs SHA-512 vs MD5</h2>
+        <p>
+          SHA-256 is the most common choice today for verifying downloads and
+          software packages. SHA-512 offers a longer digest for the same family.
+          MD5 is faster and still widely used for detecting accidental
+          corruption, though it&apos;s not considered cryptographically secure
+          against deliberate tampering.
+        </p>
+      </section>
+
+      <section>
+        <h2>Why Use a File Integrity Checker?</h2>
+        <ul>
+          <li>
+            <b>Catch corrupted downloads:</b> <br /> A hash mismatch tells you
+            immediately if a download was interrupted or damaged in transit.
+          </li>
+          <li>
+            <b>Detect tampering:</b> <br /> Comparing against a
+            publisher-provided hash confirms a file wasn&apos;t altered before
+            it reached you.
+          </li>
+          <li>
+            <b>Works on any file size:</b> <br /> Chunked streaming means
+            multi-gigabyte files are checked without loading the whole file into
+            memory.
+          </li>
+        </ul>
+      </section>
+
+      <section>
+        <h2>FAQs</h2>
+        <ul>
+          <li>
+            <b>Is this tool safe for large or sensitive files?</b> <br /> Yes.
+            Everything runs locally in your browser — files are never uploaded
+            anywhere.
+          </li>
+          <li>
+            <b>Which algorithm should I use?</b> <br /> Use whichever algorithm
+            matches the hash published by the file&apos;s source — SHA-256,
+            SHA-512, or MD5.
+          </li>
+          <li>
+            <b>Is there a file size limit?</b> <br /> No. Files are read and
+            hashed in chunks, so even very large files can be checked.
+          </li>
+          <li>
+            <b>Is my file sent to a server?</b> <br /> No. All hashing happens
+            locally in your browser. Your file never leaves your machine.
+          </li>
+        </ul>
+      </section>
+    </div>
+  );
+}

components/utils/tools-list.ts

@@ -209,4 +209,10 @@ export const tools = [
       "View, search, and filter CSV, TSV or LOG files with color-coded severity levels. Quickly scan through logs with Datadog-inspired faceted filtering.",
     link: "/utilities/csv-file-viewer",
   },
+  {
+    title: "File integrity checker",
+    description:
+      "Generate SHA-256, SHA-512, and MD5 checksums for files of any size, then verify them against a known hash to confirm the file wasn't corrupted or altered in transit.",
+    link: "/utilities/file-integrity-checker",
+  },
 ];

jest.setup.ts

@@ -1,5 +1,18 @@
 import "@testing-library/jest-dom";
 
+// jsdom's Blob (and File, which extends it) doesn't implement arrayBuffer().
+// so polyfill via FileReader, which jsdom does support.
+if (!Blob.prototype.arrayBuffer) {
+  Blob.prototype.arrayBuffer = function (this: Blob) {
+    return new Promise((resolve, reject) => {
+      const reader = new FileReader();
+      reader.onload = () => resolve(reader.result as ArrayBuffer);
+      reader.onerror = () => reject(reader.error);
+      reader.readAsArrayBuffer(this);
+    });
+  };
+}
+
 // There's no official way to mock next/navigation.
 // We just make it no-op for all tests.
 jest.mock("next/navigation", () => ({