html-tools/jwt-decoder.html at main · levups/html-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=1.0">
    <title>JWT Decoder</title>
    <link rel="stylesheet" href="common.css">
    <style>
        body {
            display: flex;
            flex-direction: column;
        }

        .jwt-input-section {
            max-width: 900px;
            margin: 0 auto 30px;
            width: 100%;
        }

        .jwt-input {
            width: 100%;
            padding: 16px;
            border: 1px solid var(--input-border);
            border-radius: var(--radius-lg);
            font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
            font-size: 0.875rem;
            background: var(--card-bg);
            color: var(--text-primary);
            box-shadow: var(--shadow-sm);
            outline: none;
            resize: vertical;
            min-height: 100px;
            transition: border-color 0.15s, box-shadow 0.15s;
        }

        .jwt-input:hover {
            border-color: var(--text-muted);
        }

        .jwt-input:focus {
            border-color: var(--input-border-focus);
            box-shadow: var(--shadow-sm), 0 0 0 3px var(--ring-color);
        }

        .jwt-input::placeholder {
            color: var(--text-secondary);
            font-family: inherit;
        }

        .output-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
            gap: 24px;
            max-width: 1400px;
            margin: 0 auto;
            width: 100%;
        }

        .output-card {
            background: var(--card-bg);
            border: 1px solid var(--card-border);
            border-radius: var(--radius-lg);
            box-shadow: var(--shadow-sm);
            overflow: hidden;
        }

        .output-card .pane-header {
            padding: 14px 20px;
        }

        .output-content {
            padding: 20px;
            font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
            font-size: 13px;
            line-height: 1.6;
            white-space: pre-wrap;
            word-break: break-word;
            min-height: 200px;
            color: var(--text-primary);
        }

        .output-content.empty {
            color: var(--text-secondary);
            font-family: inherit;
        }

        .jwt-part {
            display: inline;
        }

        .jwt-header { color: #e85555; }
        .jwt-payload { color: #9333ea; }
        .jwt-signature { color: #4d96ff; }

        .token-info {
            background: var(--card-bg);
            border: 1px solid var(--card-border);
            border-radius: var(--radius-lg);
            padding: 16px 20px;
            margin-bottom: 20px;
            font-size: 0.875rem;
            box-shadow: var(--shadow-sm);
        }

        .token-info-item {
            display: flex;
            justify-content: space-between;
            padding: 4px 0;
        }

        .token-info-label {
            color: var(--text-secondary);
        }

        .token-info-value {
            font-weight: 600;
        }

        .token-info-value.valid { color: var(--accent-mint); }
        .token-info-value.expired { color: var(--accent-coral); }

        .json-key { color: #059669; }
        .json-string { color: #9333ea; }
        .json-number { color: #e85555; }
        .json-boolean { color: #4d96ff; }
        .json-null { color: #6b7280; }

        @media (max-width: 768px) {
            .output-grid {
                grid-template-columns: 1fr;
            }
        }
    </style>
</head>
<body>

    <a href="index.html" class="back-link">
        <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
            <path d="M19 12H5M12 19l-7-7 7-7"/>
        </svg>
        All Tools
    </a>

    <header>
        <h1>JWT Decoder</h1>
        <p class="subtitle">Decode and inspect JSON Web Tokens</p>
    </header>

    <div class="jwt-input-section">
        <div id="errorBanner" class="error-message" style="margin-bottom: 16px; border-radius: 12px;"></div>
        <textarea id="jwtInput" class="jwt-input" placeholder="Paste your JWT token here...

Example: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c" spellcheck="false"></textarea>
    </div>

    <div id="tokenInfo" class="token-info jwt-input-section" style="display: none;">
        <div class="token-info-item">
            <span class="token-info-label">Algorithm</span>
            <span id="algValue" class="token-info-value">—</span>
        </div>
        <div class="token-info-item">
            <span class="token-info-label">Issued At</span>
            <span id="iatValue" class="token-info-value">—</span>
        </div>
        <div class="token-info-item">
            <span class="token-info-label">Expires</span>
            <span id="expValue" class="token-info-value">—</span>
        </div>
    </div>

    <div class="output-grid">
        <div class="output-card">
            <div class="pane-header">
                <span class="label">
                    <svg class="icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
                        <path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"></path>
                        <polyline points="14 2 14 8 20 8"></polyline>
                    </svg>
                    <span class="jwt-header">Header</span>
                </span>
                <button id="copyHeader" class="copy-btn">Copy</button>
            </div>
            <div id="headerOutput" class="output-content empty">Decoded header will appear here...</div>
        </div>

        <div class="output-card">
            <div class="pane-header">
                <span class="label">
                    <svg class="icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
                        <path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"></path>
                        <polyline points="14 2 14 8 20 8"></polyline>
                        <line x1="16" y1="13" x2="8" y2="13"></line>
                        <line x1="16" y1="17" x2="8" y2="17"></line>
                    </svg>
                    <span class="jwt-payload">Payload</span>
                </span>
                <button id="copyPayload" class="copy-btn">Copy</button>
            </div>
            <div id="payloadOutput" class="output-content empty">Decoded payload will appear here...</div>
        </div>
    </div>

    <script>
        const jwtInput = document.getElementById('jwtInput');
        const headerOutput = document.getElementById('headerOutput');
        const payloadOutput = document.getElementById('payloadOutput');
        const errorBanner = document.getElementById('errorBanner');
        const tokenInfo = document.getElementById('tokenInfo');
        const algValue = document.getElementById('algValue');
        const iatValue = document.getElementById('iatValue');
        const expValue = document.getElementById('expValue');

        let headerJson = '';
        let payloadJson = '';

        function base64UrlDecode(str) {
            // Replace URL-safe characters
            str = str.replace(/-/g, '+').replace(/_/g, '/');
            // Pad with '=' if necessary
            const pad = str.length % 4;
            if (pad) str += '='.repeat(4 - pad);
            // Decode
            return decodeURIComponent(atob(str).split('').map(c =>
                '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2)
            ).join(''));
        }

        function syntaxHighlight(json) {
            return json.replace(
                /("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g,
                match => {
                    let cls = 'json-number';
                    if (/^"/.test(match)) {
                        if (/:$/.test(match)) {
                            cls = 'json-key';
                            match = match.slice(0, -1) + '</span>:';
                            return `<span class="${cls}">${match}`;
                        } else {
                            cls = 'json-string';
                        }
                    } else if (/true|false/.test(match)) {
                        cls = 'json-boolean';
                    } else if (/null/.test(match)) {
                        cls = 'json-null';
                    }
                    return `<span class="${cls}">${match}</span>`;
                }
            );
        }

        function formatDate(timestamp) {
            if (!timestamp) return '—';
            const date = new Date(timestamp * 1000);
            return date.toLocaleString();
        }

        function decodeJWT() {
            const token = jwtInput.value.trim();

            errorBanner.style.display = 'none';
            tokenInfo.style.display = 'none';
            headerJson = '';
            payloadJson = '';

            if (!token) {
                headerOutput.textContent = 'Decoded header will appear here...';
                headerOutput.classList.add('empty');
                payloadOutput.textContent = 'Decoded payload will appear here...';
                payloadOutput.classList.add('empty');
                return;
            }

            const parts = token.split('.');
            if (parts.length !== 3) {
                errorBanner.style.display = 'block';
                errorBanner.textContent = 'Invalid JWT format. A JWT should have 3 parts separated by dots.';
                return;
            }

            try {
                // Decode header
                const header = JSON.parse(base64UrlDecode(parts[0]));
                headerJson = JSON.stringify(header, null, 2);
                headerOutput.innerHTML = syntaxHighlight(headerJson);
                headerOutput.classList.remove('empty');

                // Decode payload
                const payload = JSON.parse(base64UrlDecode(parts[1]));
                payloadJson = JSON.stringify(payload, null, 2);
                payloadOutput.innerHTML = syntaxHighlight(payloadJson);
                payloadOutput.classList.remove('empty');

                // Show token info
                tokenInfo.style.display = 'block';
                algValue.textContent = header.alg || '—';

                if (payload.iat) {
                    iatValue.textContent = formatDate(payload.iat);
                } else {
                    iatValue.textContent = '—';
                }

                if (payload.exp) {
                    const expDate = new Date(payload.exp * 1000);
                    const isExpired = expDate < new Date();
                    expValue.textContent = formatDate(payload.exp) + (isExpired ? ' (expired)' : '');
                    expValue.className = 'token-info-value ' + (isExpired ? 'expired' : 'valid');
                } else {
                    expValue.textContent = '—';
                    expValue.className = 'token-info-value';
                }

            } catch (e) {
                errorBanner.style.display = 'block';
                errorBanner.textContent = 'Failed to decode JWT: ' + e.message;
            }
        }

        function updatePageURL() {
            const input = jwtInput.value.trim();
            const newURL = new URL(window.location.href);

            if (input) {
                newURL.searchParams.set('token', input);
            } else {
                newURL.searchParams.delete('token');
            }

            history.replaceState(null, '', newURL.toString());
        }

        jwtInput.addEventListener('input', () => {
            decodeJWT();
            updatePageURL();
        });

        // Load from URL on init
        const initialToken = new URLSearchParams(window.location.search).get('token');
        if (initialToken) {
            jwtInput.value = initialToken;
            decodeJWT();
        }

        function setupCopyButton(btn, getContent) {
            btn.addEventListener('click', () => {
                const content = getContent();
                if (!content) return;
                navigator.clipboard.writeText(content).then(() => {
                    const originalText = btn.textContent;
                    btn.textContent = 'Copied!';
                    btn.classList.add('copied');
                    setTimeout(() => {
                        btn.textContent = originalText;
                        btn.classList.remove('copied');
                    }, 2000);
                });
            });
        }

        setupCopyButton(document.getElementById('copyHeader'), () => headerJson);
        setupCopyButton(document.getElementById('copyPayload'), () => payloadJson);
    </script>
</body>
</html>