diff --git a/functions/api/submit-gap.js b/functions/api/submit-gap.js
index e566ca4..fa38156 100644
--- a/functions/api/submit-gap.js
+++ b/functions/api/submit-gap.js
@@ -65,7 +65,7 @@ function json(obj, status, extra = {}) {
   return new Response(JSON.stringify(obj), { status, headers: { "Content-Type": "application/json", ...extra } });
 }
 
-async function sha256(str) {
+export async function sha256(str) {
   const buf = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(str));
   return [...new Uint8Array(buf)].map((b) => b.toString(16).padStart(2, "0")).join("");
 }
diff --git a/functions/api/submit-gap.test.js b/functions/api/submit-gap.test.js
new file mode 100644
index 0000000..13a5ae7
--- /dev/null
+++ b/functions/api/submit-gap.test.js
@@ -0,0 +1,35 @@
+import { describe, it, expect } from 'vitest';
+import { sha256 } from './submit-gap.js';
+
+describe('sha256', () => {
+  it('should compute the correct SHA-256 hash for a known IP string', async () => {
+    const input = '127.0.0.1';
+    // SHA-256 of "127.0.0.1"
+    const expected = '12ca17b49af2289436f303e0166030a21e525d266e209267433801a8fd4071a0';
+    const result = await sha256(input);
+    expect(result).toBe(expected);
+  });
+
+  it('should compute the correct SHA-256 hash for an empty string', async () => {
+    const input = '';
+    // SHA-256 of ""
+    const expected = 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855';
+    const result = await sha256(input);
+    expect(result).toBe(expected);
+  });
+
+  it('should correctly handle a string with non-ASCII characters', async () => {
+    const input = 'hello world 🚀';
+    // SHA-256 of "hello world 🚀"
+    const expected = '7794bdd7454346eb21712d6fa26d63df3db615cd34f20d9ad5cd455897d7ca8a';
+    const result = await sha256(input);
+    expect(result).toBe(expected);
+  });
+
+  it('should produce deterministic output for the same input', async () => {
+    const input = 'some random string to test determinism';
+    const result1 = await sha256(input);
+    const result2 = await sha256(input);
+    expect(result1).toBe(result2);
+  });
+});
diff --git a/package-lock.json b/package-lock.json
index 440586a..27483e3 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -22,7 +22,8 @@
         "wrangler": "^4.80.0"
       },
       "devDependencies": {
-        "gray-matter": "^4.0.3"
+        "gray-matter": "^4.0.3",
+        "vitest": "^4.1.10"
       },
       "engines": {
         "node": ">=22.12.0"
@@ -1916,6 +1917,13 @@
       "integrity": "sha512-BMq1K3DsElxDWawkX6eLg9+CKJrTVGCBAWVuHXVUV2u0s2711qiChLSId6ikYPfxhdYocLNt3wWwSvDiTvFabw==",
       "license": "CC0-1.0"
     },
+    "node_modules/@standard-schema/spec": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/@standard-schema/spec/-/spec-1.1.0.tgz",
+      "integrity": "sha512-l2aFy5jALhniG5HgqrD6jXLi/rUWrKvqN/qJx6yoJsgKhblVd+iqqU4RCXavm/jPityDo5TCvKMnpjKnOriy0w==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@tailwindcss/node": {
       "version": "4.2.2",
       "resolved": "https://registry.npmjs.org/@tailwindcss/node/-/node-4.2.2.tgz",
@@ -2173,6 +2181,17 @@
         "vite": "^5.2.0 || ^6 || ^7 || ^8"
       }
     },
+    "node_modules/@types/chai": {
+      "version": "5.2.3",
+      "resolved": "https://registry.npmjs.org/@types/chai/-/chai-5.2.3.tgz",
+      "integrity": "sha512-Mw558oeA9fFbv65/y4mHtXDs9bPnFMZAL/jxdPFUpOHHIXX91mcgEHbS5Lahr+pwZFR8A7GQleRWeI6cGFC2UA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/deep-eql": "*",
+        "assertion-error": "^2.0.1"
+      }
+    },
     "node_modules/@types/debug": {
       "version": "4.1.13",
       "resolved": "https://registry.npmjs.org/@types/debug/-/debug-4.1.13.tgz",
@@ -2182,6 +2201,13 @@
         "@types/ms": "*"
       }
     },
+    "node_modules/@types/deep-eql": {
+      "version": "4.0.2",
+      "resolved": "https://registry.npmjs.org/@types/deep-eql/-/deep-eql-4.0.2.tgz",
+      "integrity": "sha512-c9h9dVVMigMPc4bwTvC5dxqtqJZwQPePsWjPlpSOnojbor6pGqdk541lfA7AqFQr5pB1BRdq0juY9db81BwyFw==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/estree": {
       "version": "1.0.8",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz",
@@ -2266,6 +2292,129 @@
       "integrity": "sha512-WmoN8qaIAo7WTYWbAZuG8PYEhn5fkz7dZrqTBZ7dtt//lL2Gwms1IcnQ5yHqjDfX8Ft5j4YzDM23f87zBfDe9g==",
       "license": "ISC"
     },
+    "node_modules/@vitest/expect": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/expect/-/expect-4.1.10.tgz",
+      "integrity": "sha512-YsCn+qAk1GWjQOWFEsEcL2gNQ0zmVmQu3T03qP6UyjhtmdtwtbuI+DASn/7iQB3HGTXkdBwGddzxPlmiql5vlA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@standard-schema/spec": "^1.1.0",
+        "@types/chai": "^5.2.2",
+        "@vitest/spy": "4.1.10",
+        "@vitest/utils": "4.1.10",
+        "chai": "^6.2.2",
+        "tinyrainbow": "^3.1.0"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      }
+    },
+    "node_modules/@vitest/mocker": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/mocker/-/mocker-4.1.10.tgz",
+      "integrity": "sha512-v0xaezt+DKEmKfaxg133ldzADrwLGd7Ze1MfQQTYfvs8OqZIwbxyxaYURivwV7sWy5fqn3rH5uOrSp07bp44Ow==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@vitest/spy": "4.1.10",
+        "estree-walker": "^3.0.3",
+        "magic-string": "^0.30.21"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      },
+      "peerDependencies": {
+        "msw": "^2.4.9",
+        "vite": "^6.0.0 || ^7.0.0 || ^8.0.0"
+      },
+      "peerDependenciesMeta": {
+        "msw": {
+          "optional": true
+        },
+        "vite": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/@vitest/mocker/node_modules/estree-walker": {
+      "version": "3.0.3",
+      "resolved": "https://registry.npmjs.org/estree-walker/-/estree-walker-3.0.3.tgz",
+      "integrity": "sha512-7RUKfXgSMMkzt6ZuXmqapOurLGPPfgj6l9uRZ7lRGolvk0y2yocc35LdcxKC5PQZdn2DMqioAQ2NoWcrTKmm6g==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/estree": "^1.0.0"
+      }
+    },
+    "node_modules/@vitest/pretty-format": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/pretty-format/-/pretty-format-4.1.10.tgz",
+      "integrity": "sha512-W1HsjSH4MXQ9YfmmhLAoIYf1HRfekQCGngeIgcei6MP5QQGWUe0gkopdZQaVCFO+JDJMrAJGwa5pRpNpvy4P8Q==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "tinyrainbow": "^3.1.0"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      }
+    },
+    "node_modules/@vitest/runner": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/runner/-/runner-4.1.10.tgz",
+      "integrity": "sha512-IKI6kpIH+LmpROplyLwBBaCfMgOZOMsygVa6BARD6ahA04VRuJSa6OaVG7kRvSEMD870Vd91rSSw0eegtWyLGg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@vitest/utils": "4.1.10",
+        "pathe": "^2.0.3"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      }
+    },
+    "node_modules/@vitest/snapshot": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/snapshot/-/snapshot-4.1.10.tgz",
+      "integrity": "sha512-xRkfOT1qpTAi/Ti4Y1LtfRc3kEuqxGw59eN2jN9pRWMtS/XDevekhcFSqvQqjUNGksfjMJu3Y+oJ+4Ypn2OaJw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@vitest/pretty-format": "4.1.10",
+        "@vitest/utils": "4.1.10",
+        "magic-string": "^0.30.21",
+        "pathe": "^2.0.3"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      }
+    },
+    "node_modules/@vitest/spy": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/spy/-/spy-4.1.10.tgz",
+      "integrity": "sha512-PLf/Ugvoq5wO/b4rwYCR1h2PSIdXz7wnkQFMiUpLdtM7l6pqVFcQIBEHyT1+l+cj7mNwAfZHzqXqDyjvOuwbDw==",
+      "dev": true,
+      "license": "MIT",
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      }
+    },
+    "node_modules/@vitest/utils": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/@vitest/utils/-/utils-4.1.10.tgz",
+      "integrity": "sha512-fy9am/HWxbaGt/Sawrp90vt6Y6jQwf1RX77cz3uwoJwJVMli/e1IEwRPnMNJ7vKfPTwo0diXifkpPvwH9v7nGA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@vitest/pretty-format": "4.1.10",
+        "convert-source-map": "^2.0.0",
+        "tinyrainbow": "^3.1.0"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      }
+    },
     "node_modules/acorn": {
       "version": "8.16.0",
       "resolved": "https://registry.npmjs.org/acorn/-/acorn-8.16.0.tgz",
@@ -2355,6 +2504,16 @@
         "url": "https://github.com/sponsors/wooorm"
       }
     },
+    "node_modules/assertion-error": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/assertion-error/-/assertion-error-2.0.1.tgz",
+      "integrity": "sha512-Izi8RQcffqCeNVgFigKli1ssklIbpHnCYc6AknXGYoB6grJqyeby7jv12JUQgmTAnIDnbck1uxksT4dzN3PWBA==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=12"
+      }
+    },
     "node_modules/astring": {
       "version": "1.9.0",
       "resolved": "https://registry.npmjs.org/astring/-/astring-1.9.0.tgz",
@@ -2495,6 +2654,16 @@
         "url": "https://github.com/sponsors/wooorm"
       }
     },
+    "node_modules/chai": {
+      "version": "6.2.2",
+      "resolved": "https://registry.npmjs.org/chai/-/chai-6.2.2.tgz",
+      "integrity": "sha512-NUPRluOfOiTKBKvWPtSD4PhFvWCqOi0BGStNWs57X9js7XGTprSmFoz5F0tWhR4WPjNeR9jXqdC7/UpSJTnlRg==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/character-entities": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/character-entities/-/character-entities-2.0.2.tgz",
@@ -2612,6 +2781,13 @@
         "node": ">= 18"
       }
     },
+    "node_modules/convert-source-map": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/convert-source-map/-/convert-source-map-2.0.0.tgz",
+      "integrity": "sha512-Kvp459HrV2FEJ1CAsi1Ku+MY3kasH19TFykTz2xWmMeq6bk2NU3XXvfJ+Q61m0xktWwt+1HSYf3JZsTms3aRJg==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/cookie": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/cookie/-/cookie-1.1.1.tgz",
@@ -3126,6 +3302,16 @@
       "integrity": "sha512-mlsTRyGaPBjPedk6Bvw+aqbsXDtoAyAzm5MO7JgU+yVRyMQ5O8bD4Kcci7BS85f93veegeCPkL8R4GLClnjLFw==",
       "license": "MIT"
     },
+    "node_modules/expect-type": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/expect-type/-/expect-type-1.4.0.tgz",
+      "integrity": "sha512-KfYbmpRm0VbLjEvVa9yGwCi9GI34xvi7A/HXYWQO65CSD2u3MczUJSuwXKFIxlGsgBQizV9q5J9NHj4VG0n+pA==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "engines": {
+        "node": ">=12.0.0"
+      }
+    },
     "node_modules/extend": {
       "version": "3.0.2",
       "resolved": "https://registry.npmjs.org/extend/-/extend-3.0.2.tgz",
@@ -5946,6 +6132,13 @@
         "node": ">=20"
       }
     },
+    "node_modules/siginfo": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/siginfo/-/siginfo-2.0.0.tgz",
+      "integrity": "sha512-ybx0WO1/8bSBLEWXZvEd7gMW3Sn3JFlW3TvX1nREbDLRNQNaeNN8WK0meBwPdAaOI7TtRRRJn/Es1zhrrCHu7g==",
+      "dev": true,
+      "license": "ISC"
+    },
     "node_modules/sisteransi": {
       "version": "1.0.5",
       "resolved": "https://registry.npmjs.org/sisteransi/-/sisteransi-1.0.5.tgz",
@@ -6018,6 +6211,20 @@
       "dev": true,
       "license": "BSD-3-Clause"
     },
+    "node_modules/stackback": {
+      "version": "0.0.2",
+      "resolved": "https://registry.npmjs.org/stackback/-/stackback-0.0.2.tgz",
+      "integrity": "sha512-1XMJE5fQo1jGH6Y/7ebnwPOBEkIEnT4QF32d5R1+VXdXveM0IBMJt8zfaxX1P3QhVwrYe+576+jkANtSS2mBbw==",
+      "dev": true,
+      "license": "MIT"
+    },
+    "node_modules/std-env": {
+      "version": "4.2.0",
+      "resolved": "https://registry.npmjs.org/std-env/-/std-env-4.2.0.tgz",
+      "integrity": "sha512-oCUKSupKTHX53EyjDtuZQ64pjLJ6yYCtpmEw0goYxtjG9KpbRe8KAsl2tBUGU9DyMcJ0RwJ8GqJAFzMXcXW1Rw==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/stream-replace-string": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/stream-replace-string/-/stream-replace-string-2.0.0.tgz",
@@ -6143,6 +6350,13 @@
       "integrity": "sha512-pkY1fj1cKHb2seWDy0B16HeWyczlJA9/WW3u3c4z/NiWDsO3DOU5D7nhTLE9CF0yXv/QZFY7sEJmj24dK+Rrqw==",
       "license": "MIT"
     },
+    "node_modules/tinybench": {
+      "version": "2.9.0",
+      "resolved": "https://registry.npmjs.org/tinybench/-/tinybench-2.9.0.tgz",
+      "integrity": "sha512-0+DUvqWMValLmha6lr4kD8iAMK1HzV0/aKnCtWb9v9641TnP/MFb7Pc2bxoxQjTXAErryXVgUOfv2YqNllqGeg==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/tinyclip": {
       "version": "0.1.12",
       "resolved": "https://registry.npmjs.org/tinyclip/-/tinyclip-0.1.12.tgz",
@@ -6177,6 +6391,16 @@
         "url": "https://github.com/sponsors/SuperchupuDev"
       }
     },
+    "node_modules/tinyrainbow": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/tinyrainbow/-/tinyrainbow-3.1.0.tgz",
+      "integrity": "sha512-Bf+ILmBgretUrdJxzXM0SgXLZ3XfiaUuOj/IKQHuTXip+05Xn+uyEYdVg0kYDipTBcLrCVyUzAPz7QmArb0mmw==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=14.0.0"
+      }
+    },
     "node_modules/trim-lines": {
       "version": "3.0.1",
       "resolved": "https://registry.npmjs.org/trim-lines/-/trim-lines-3.0.1.tgz",
@@ -6663,6 +6887,96 @@
         }
       }
     },
+    "node_modules/vitest": {
+      "version": "4.1.10",
+      "resolved": "https://registry.npmjs.org/vitest/-/vitest-4.1.10.tgz",
+      "integrity": "sha512-R9jUTe5S4Qb0HCd4TNqpC7oGcrMssMRGXLW80ubjWsW9VH5GF8y1Y0SFLY9AbqSk6nt0PnOx4H4WNJYZ13GUPw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@vitest/expect": "4.1.10",
+        "@vitest/mocker": "4.1.10",
+        "@vitest/pretty-format": "4.1.10",
+        "@vitest/runner": "4.1.10",
+        "@vitest/snapshot": "4.1.10",
+        "@vitest/spy": "4.1.10",
+        "@vitest/utils": "4.1.10",
+        "es-module-lexer": "^2.0.0",
+        "expect-type": "^1.3.0",
+        "magic-string": "^0.30.21",
+        "obug": "^2.1.1",
+        "pathe": "^2.0.3",
+        "picomatch": "^4.0.3",
+        "std-env": "^4.0.0-rc.1",
+        "tinybench": "^2.9.0",
+        "tinyexec": "^1.0.2",
+        "tinyglobby": "^0.2.15",
+        "tinyrainbow": "^3.1.0",
+        "vite": "^6.0.0 || ^7.0.0 || ^8.0.0",
+        "why-is-node-running": "^2.3.0"
+      },
+      "bin": {
+        "vitest": "vitest.mjs"
+      },
+      "engines": {
+        "node": "^20.0.0 || ^22.0.0 || >=24.0.0"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      },
+      "peerDependencies": {
+        "@edge-runtime/vm": "*",
+        "@opentelemetry/api": "^1.9.0",
+        "@types/node": "^20.0.0 || ^22.0.0 || >=24.0.0",
+        "@vitest/browser-playwright": "4.1.10",
+        "@vitest/browser-preview": "4.1.10",
+        "@vitest/browser-webdriverio": "4.1.10",
+        "@vitest/coverage-istanbul": "4.1.10",
+        "@vitest/coverage-v8": "4.1.10",
+        "@vitest/ui": "4.1.10",
+        "happy-dom": "*",
+        "jsdom": "*",
+        "vite": "^6.0.0 || ^7.0.0 || ^8.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@edge-runtime/vm": {
+          "optional": true
+        },
+        "@opentelemetry/api": {
+          "optional": true
+        },
+        "@types/node": {
+          "optional": true
+        },
+        "@vitest/browser-playwright": {
+          "optional": true
+        },
+        "@vitest/browser-preview": {
+          "optional": true
+        },
+        "@vitest/browser-webdriverio": {
+          "optional": true
+        },
+        "@vitest/coverage-istanbul": {
+          "optional": true
+        },
+        "@vitest/coverage-v8": {
+          "optional": true
+        },
+        "@vitest/ui": {
+          "optional": true
+        },
+        "happy-dom": {
+          "optional": true
+        },
+        "jsdom": {
+          "optional": true
+        },
+        "vite": {
+          "optional": false
+        }
+      }
+    },
     "node_modules/web-namespaces": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/web-namespaces/-/web-namespaces-2.0.1.tgz",
@@ -6682,6 +6996,23 @@
         "node": ">=4"
       }
     },
+    "node_modules/why-is-node-running": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/why-is-node-running/-/why-is-node-running-2.3.0.tgz",
+      "integrity": "sha512-hUrmaWBdVDcxvYqnyh09zunKzROWjbZTiNy8dBEjkS7ehEDQibXJ7XvlmtbwuTclUiIyN+CyXQD4Vmko8fNm8w==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "siginfo": "^2.0.0",
+        "stackback": "0.0.2"
+      },
+      "bin": {
+        "why-is-node-running": "cli.js"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/workerd": {
       "version": "1.20260401.1",
       "resolved": "https://registry.npmjs.org/workerd/-/workerd-1.20260401.1.tgz",
diff --git a/package.json b/package.json
index 8e04d20..fca48b1 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,8 @@
     "generate-types": "wrangler types",
     "seo:audit": "node seo-audit.mjs",
     "seo:crawl": "node seo-crawl-audit.mjs",
-    "gsc:coverage": "node gsc-coverage.mjs"
+    "gsc:coverage": "node gsc-coverage.mjs",
+    "test": "vitest run"
   },
   "dependencies": {
     "@astrojs/cloudflare": "^13.1.7",
@@ -33,6 +34,7 @@
     "vite": "^7"
   },
   "devDependencies": {
-    "gray-matter": "^4.0.3"
+    "gray-matter": "^4.0.3",
+    "vitest": "^4.1.10"
   }
 }