tools/cors-header-analyzer.html at main · jubilancy/tools · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>CORS Header Analyzer | tools.eliana.lol</title>
  <link rel="stylesheet" href="global.css" />
  <link rel="icon" type="image/x-icon" href="favicon.svg" />
  <style>
    .container {
      display: flex;
      flex-direction: column;
      gap: 1.5rem;
    }

    .input-group {
      display: flex;
      flex-direction: column;
      gap: 0.5rem;
    }

    .input-label {
      font-size: 0.85rem;
      font-weight: bold;
      text-transform: uppercase;
      color: var(--puny);
      letter-spacing: 0.05em;
    }

    .button-group {
      display: flex;
      flex-wrap: wrap;
      gap: 0.75rem;
    }

    button {
      flex: 0 1 auto;
      min-width: 120px;
      padding: 10px;
      cursor: pointer;
      font-family: monospace;
      border: 1px solid var(--text);
      background: var(--bg);
      color: var(--text);
      border-radius: 4px;
      transition: all 150ms;
    }

    button:hover {
      background-color: var(--hover);
      border-color: var(--accent);
    }

    button.primary {
      border-color: var(--accent);
      font-weight: bold;
      color: var(--accent);
    }

    textarea,
    input[type="text"] {
      width: 100%;
      font-family: monospace;
      padding: 10px;
      border: 1px solid var(--puny);
      background: var(--bg);
      color: var(--text);
      box-sizing: border-box;
      border-radius: 4px;
      font-size: 0.95rem;
    }

    textarea:focus,
    input[type="text"]:focus {
      outline: none;
      border-color: var(--accent);
    }

    textarea {
      min-height: 180px;
      resize: vertical;
    }

    .status {
      padding: 0.75rem 1rem;
      border-radius: 4px;
      margin: 0.5rem 0;
      display: none;
      font-size: 0.9rem;
    }

    .status.show {
      display: block;
    }

    .status.success {
      background-color: rgba(16, 185, 129, 0.1);
      border-left: 3px solid var(--accent);
      color: var(--accent);
    }

    .status.error {
      background-color: rgba(239, 68, 68, 0.1);
      border-left: 3px solid #ef4444;
      color: #ef4444;
    }

    .info-box {
      padding: 1rem;
      background-color: var(--highlight);
      border-left: 3px solid var(--accent);
      font-size: 0.9rem;
      line-height: 1.6;
    }

    @media (max-width: 600px) {
      .button-group {
        flex-direction: column;
      }

      button {
        width: 100%;
      }
      .origin-row {
        flex-direction: column;
        align-items: stretch !important;
      }
    }

    /* Tool-specific styles */
    .origin-row {
      display: flex;
      gap: 0.75rem;
      align-items: center;
    }

    .origin-row input {
      flex: 1;
    }

    .verdict-card {
      border: 1px solid var(--puny);
      border-radius: 4px;
      padding: 12px 14px;
      display: flex;
      gap: 10px;
      align-items: flex-start;
    }

    .verdict-card.pass {
      border-left: 4px solid var(--accent);
    }

    .verdict-card.fail {
      border-left: 4px solid #ef4444;
    }

    .verdict-icon {
      font-weight: bold;
      font-size: 1.2rem;
      line-height: 1.2;
    }

    .verdict-card.pass .verdict-icon { color: var(--accent); }
    .verdict-card.fail .verdict-icon { color: #ef4444; }

    .verdict-text {
      font-size: 0.9rem;
    }

    .breakdown-list {
      display: flex;
      flex-direction: column;
      gap: 6px;
    }

    .breakdown-item {
      display: flex;
      gap: 10px;
      font-size: 0.85rem;
      padding: 6px 0;
      border-bottom: 1px solid var(--hover);
    }

    .breakdown-item .header-name {
      font-family: monospace;
      font-weight: bold;
      min-width: 220px;
    }

    .breakdown-item .header-explain {
      color: var(--text);
    }
  </style>
</head>
<body>
  <nav>
    <div class="left">
      <a href="index.html">home</a> | <a href="extra.html">extra</a> |
      <a href="credits.html">credits</a> |
      <a href="changelog.html">logs</a>
    </div>
    <div class="right">
      <button id="theme-toggle">[theme]</button> |
      <a href="https://eliana.lol">site</a>
    </div>
  </nav>

  <main>
    <h1>CORS Header Analyzer</h1>
    <p class="puny">Paste response headers and get a plain-English breakdown of what the CORS policy allows and blocks.</p>

    <div class="container">
      <div class="input-group">
        <span class="input-label">Response headers</span>
        <textarea id="headers-input" placeholder="Access-Control-Allow-Origin: https://example.com
Access-Control-Allow-Methods: GET, POST
Access-Control-Allow-Headers: Content-Type, Authorization
Access-Control-Allow-Credentials: true">Access-Control-Allow-Origin: https://myapp.com
Access-Control-Allow-Methods: GET, POST, PUT
Access-Control-Allow-Headers: Content-Type, Authorization
Access-Control-Allow-Credentials: true
Access-Control-Max-Age: 3600</textarea>
      </div>

      <div class="input-group">
        <span class="input-label">Simulate a request from</span>
        <div class="origin-row">
          <input type="text" id="origin-input" value="https://myapp.com" placeholder="https://your-frontend.com" />
          <span class="puny">using</span>
          <select id="method-select" style="width: auto; font-family: monospace; padding: 8px; border: 1px solid var(--puny); background: var(--bg); color: var(--text); border-radius: 4px;">
            <option>GET</option>
            <option>POST</option>
            <option>PUT</option>
            <option>DELETE</option>
            <option>PATCH</option>
          </select>
        </div>
      </div>

      <div class="input-group">
        <span class="input-label">Verdict</span>
        <div id="verdict-wrap"></div>
      </div>

      <div class="input-group">
        <span class="input-label">Header-by-header breakdown</span>
        <div class="breakdown-list" id="breakdown-list"></div>
      </div>

      <div class="info-box">
        <strong>Tip:</strong> The browser — not the server — enforces CORS. These headers only matter for cross-origin requests; same-origin requests are never blocked regardless of what's set here.
      </div>

      <div class="status" id="status"></div>
    </div>
  </main>

  <footer style="margin-top: 4rem; text-align: center" class="puny">
    © 2026 eliana.lol • <a href="credits.html">credits</a>
  </footer>

  <!-- Theme Toggle Script (Required for all tools) -->
  <script>
    const html = document.documentElement;
    const toggle = document.getElementById('theme-toggle');
    const saved =
      localStorage.getItem('theme') ||
      (window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light');

    html.setAttribute('data-theme', saved);
    if (toggle) toggle.innerText = saved === 'dark' ? '[light]' : '[dark]';

    if (toggle) {
      toggle.onclick = () => {
        const now = html.getAttribute('data-theme');
        const next = now === 'dark' ? 'light' : 'dark';
        html.setAttribute('data-theme', next);
        localStorage.setItem('theme', next);
        toggle.innerText = next === 'dark' ? '[light]' : '[dark]';
      };
    }
  </script>

  <!-- Tool-specific script -->
  <script>
    function showStatus(message, type = 'success') {
      const status = document.getElementById('status');
      status.textContent = message;
      status.className = `status show ${type}`;
      setTimeout(() => status.classList.remove('show'), 2000);
    }

    function parseHeaders(text) {
      const headers = {};
      text.split('\n').forEach((line) => {
        const idx = line.indexOf(':');
        if (idx === -1) return;
        const key = line.slice(0, idx).trim().toLowerCase();
        const value = line.slice(idx + 1).trim();
        if (key) headers[key] = value;
      });
      return headers;
    }

    function explainHeader(key, value) {
      switch (key) {
        case 'access-control-allow-origin':
          if (value === '*') return 'Allows requests from any origin. Cannot be combined with credentials: true — browsers will reject that combination.';
          return `Allows cross-origin requests only from the origin "${value}". Requests from any other origin will be blocked by the browser.`;
        case 'access-control-allow-methods':
          return `Permits these HTTP methods on cross-origin requests: ${value}. Any method not listed here will fail preflight for non-simple requests.`;
        case 'access-control-allow-headers':
          return `Permits these request headers to be sent cross-origin: ${value}. Custom headers not listed here will be blocked during preflight.`;
        case 'access-control-allow-credentials':
          return value.toLowerCase() === 'true'
            ? 'Allows cookies and HTTP auth credentials to be sent with cross-origin requests. Requires Allow-Origin to be a specific origin, not "*".'
            : 'Credentials (cookies, auth headers) will not be included in cross-origin requests.';
        case 'access-control-expose-headers':
          return `Makes these response headers readable by client-side JavaScript: ${value}. Without this, only a small default set of headers is visible to scripts.`;
        case 'access-control-max-age':
          return `Caches the preflight (OPTIONS) response for ${value} seconds, reducing repeated preflight requests during that window.`;
        case 'vary':
          return `Tells caches that the response varies by this header (commonly "Origin") — important so cached CORS responses aren't served to the wrong origin.`;
        default:
          return 'Not a standard CORS header — included here for reference only.';
      }
    }

    function analyze() {
      const headersText = document.getElementById('headers-input').value;
      const origin = document.getElementById('origin-input').value.trim();
      const method = document.getElementById('method-select').value;

      const headers = parseHeaders(headersText);
      const verdictWrap = document.getElementById('verdict-wrap');
      const breakdownList = document.getElementById('breakdown-list');

      const allowOrigin = headers['access-control-allow-origin'];
      const allowMethods = headers['access-control-allow-methods'];
      const allowCredentials = headers['access-control-allow-credentials'];

      const issues = [];
      const passes = [];

      if (!allowOrigin) {
        issues.push('No Access-Control-Allow-Origin header is present, so the browser will block this cross-origin request entirely.');
      } else if (allowOrigin === '*') {
        if (allowCredentials && allowCredentials.toLowerCase() === 'true') {
          issues.push('Allow-Origin is "*" combined with Allow-Credentials: true — browsers reject this exact combination, so credentialed requests will fail regardless of origin.');
        } else {
          passes.push(`Any origin (including "${origin || 'your origin'}") is allowed to read the response.`);
        }
      } else if (origin && allowOrigin.toLowerCase() !== origin.toLowerCase()) {
        issues.push(`Allow-Origin is set to "${allowOrigin}", which does not match the simulated origin "${origin}" — this request would be blocked.`);
      } else if (origin) {
        passes.push(`Origin "${origin}" matches the allowed origin exactly.`);
      }

      if (allowMethods) {
        const methodsList = allowMethods.split(',').map((m) => m.trim().toUpperCase());
        if (!methodsList.includes(method)) {
          issues.push(`Method "${method}" is not in the allowed methods list (${allowMethods}) — a preflight request would fail for this method.`);
        } else {
          passes.push(`Method "${method}" is explicitly allowed.`);
        }
      } else if (!['GET', 'HEAD', 'POST'].includes(method)) {
        issues.push(`No Access-Control-Allow-Methods header found, and "${method}" is not a CORS-safelisted method — preflight will likely fail.`);
      }

      verdictWrap.innerHTML = '';
      if (issues.length === 0) {
        const card = document.createElement('div');
        card.className = 'verdict-card pass';
        card.innerHTML = `<span class="verdict-icon">✓</span><span class="verdict-text">This request would likely succeed. ${passes.join(' ')}</span>`;
        verdictWrap.appendChild(card);
      } else {
        issues.forEach((issue) => {
          const card = document.createElement('div');
          card.className = 'verdict-card fail';
          card.innerHTML = `<span class="verdict-icon">✕</span><span class="verdict-text">${issue}</span>`;
          verdictWrap.appendChild(card);
        });
        if (passes.length > 0) {
          const card = document.createElement('div');
          card.className = 'verdict-card pass';
          card.innerHTML = `<span class="verdict-icon">✓</span><span class="verdict-text">${passes.join(' ')}</span>`;
          verdictWrap.appendChild(card);
        }
      }

      breakdownList.innerHTML = '';
      const knownOrder = [
        'access-control-allow-origin',
        'access-control-allow-methods',
        'access-control-allow-headers',
        'access-control-allow-credentials',
        'access-control-expose-headers',
        'access-control-max-age',
        'vary'
      ];

      const allKeys = Object.keys(headers).sort((a, b) => {
        const ai = knownOrder.indexOf(a);
        const bi = knownOrder.indexOf(b);
        if (ai === -1 && bi === -1) return a.localeCompare(b);
        if (ai === -1) return 1;
        if (bi === -1) return -1;
        return ai - bi;
      });

      if (allKeys.length === 0) {
        breakdownList.innerHTML = '<p class="puny">Paste headers above to see a breakdown.</p>';
        return;
      }

      allKeys.forEach((key) => {
        const item = document.createElement('div');
        item.className = 'breakdown-item';
        item.innerHTML = `
          <span class="header-name">${key}</span>
          <span class="header-explain">${explainHeader(key, headers[key])}</span>
        `;
        breakdownList.appendChild(item);
      });
    }

    document.getElementById('headers-input').addEventListener('input', analyze);
    document.getElementById('origin-input').addEventListener('input', analyze);
    document.getElementById('method-select').addEventListener('change', analyze);

    analyze();
  </script>
</body>
</html>