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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 — DevDunia</title>
<meta name="description" content="Decode and verify JWT tokens. Free online JWT decoder with header and payload analysis for developers.">
<meta property="og:type" content="website">
<meta property="og:url" content="https://devdunia.com/production/jwt-decoder.html">
<meta property="og:title" content="JWT Decoder — DevDunia">
<meta property="og:description" content="Decode and verify JWT tokens. Free online JWT decoder with header and payload analysis.">
<meta property="og:image" content="https://devdunia.com/images/logo.png">
<link rel="preconnect" href="https://fonts.googleapis.com">
<link href="https://fonts.googleapis.com/css2?family=Bangers&family=Comic+Neue:wght@400;700&family=Space+Mono:wght@400;700&display=swap" rel="stylesheet">
<style>
:root {
--ink: #1a1410;
--paper: #fdf3e3;
--paper2: #fbe9cc;
--red: #e63946;
--blue: #1d6fb8;
--yellow: #ffd23f;
--green: #3fa34d;
--pink: #ff6b9d;
--purple: #8a4fff;
--orange: #ff8c42;
}
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
body {
font-family: 'Comic Neue', cursive;
font-weight: 400;
color: var(--ink);
background-color: var(--paper);
background-image: radial-gradient(var(--ink) 0.5px, transparent 0.6px);
background-size: 14px 14px;
background-attachment: fixed;
min-height: 100vh;
}
.paper-overlay {
position: fixed;
inset: 0;
background: rgba(253,243,227,.78);
pointer-events: none;
z-index: 0;
}
.page-wrap {
position: relative;
z-index: 1;
max-width: 1240px;
margin: 0 auto;
padding: 20px 32px 60px;
}
/* HERO */
.hero {
display: flex; align-items: flex-start; gap: 20px;
background: var(--paper2);
border: 4px solid var(--ink); border-radius: 6px;
box-shadow: 7px 7px 0 var(--ink);
padding: 20px 24px; margin-bottom: 28px;
transform: rotate(-0.4deg);
}
.hero-icon { font-size: 3rem; line-height: 1; flex-shrink: 0; filter: drop-shadow(3px 3px 0 var(--ink)); }
.hero-text h1 { font-family: 'Bangers', cursive; font-size: 2.8rem; letter-spacing: 2px; color: var(--blue); -webkit-text-stroke: 1px var(--ink); text-shadow: 4px 4px 0 var(--ink); line-height: 1; text-transform: uppercase; }
.hero-text p { font-size: .95rem; margin-top: 6px; line-height: 1.5; max-width: 480px; }
.hero-badges { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 10px; }
.badge { font-family: 'Space Mono', monospace; font-size: .65rem; font-weight: 700; padding: 3px 8px; border: 2px solid var(--ink); border-radius: 4px; box-shadow: 2px 2px 0 var(--ink); }
.badge-blue { background: var(--blue); color: #fff; }
.badge-green { background: var(--green); color: #fff; }
.badge-yellow { background: var(--yellow); color: var(--ink); }
.badge-red { background: var(--red); color: #fff; }
.badge-purple { background: var(--purple); color: #fff; }
.badge-orange { background: var(--orange); color: #fff; }
/* PANEL */
.panel { background: var(--paper); border: 4px solid var(--ink); border-radius: 6px; box-shadow: 7px 7px 0 var(--ink); overflow: hidden; margin-bottom: 22px; }
.panel-header { background: var(--ink); color: var(--yellow); font-family: 'Bangers', cursive; font-size: 1.2rem; letter-spacing: 2px; padding: 8px 16px; display: flex; align-items: center; justify-content: space-between; gap: 10px; }
.panel-header .panel-tag { font-family: 'Space Mono', monospace; font-size: .65rem; font-weight: 700; background: var(--yellow); color: var(--ink); padding: 2px 7px; border-radius: 3px; }
.panel-body { padding: 18px 20px; }
/* TOKEN PARTS DISPLAY */
.token-display {
font-family: 'Space Mono', monospace;
font-size: .78rem;
line-height: 1.7;
word-break: break-all;
background: #fff;
border: 3px solid var(--ink);
border-radius: 6px;
padding: 12px 14px;
box-shadow: 3px 3px 0 var(--ink);
margin-bottom: 14px;
}
.token-header-part { color: var(--green); }
.token-payload-part { color: var(--purple); }
.token-sig-part { color: var(--orange); }
/* INFO GRID */
.info-grid {
display: grid;
grid-template-columns: repeat(3, 1fr);
gap: 10px;
margin-bottom: 18px;
}
.info-chip {
background: var(--paper2);
border: 3px solid var(--ink);
border-radius: 6px;
box-shadow: 3px 3px 0 var(--ink);
padding: 8px 12px;
}
.info-chip-label { font-family: 'Bangers', cursive; font-size: .85rem; letter-spacing: 1px; color: var(--ink); opacity: .7; }
.info-chip-value { font-family: 'Space Mono', monospace; font-size: .78rem; font-weight: 700; margin-top: 2px; }
/* TEXTAREA */
.comic-textarea {
width: 100%;
background: #fff;
border: 3px solid var(--ink);
border-radius: 6px;
padding: 12px 14px;
font-family: 'Space Mono', monospace;
font-size: .82rem;
color: var(--ink);
line-height: 1.6;
resize: vertical;
min-height: 130px;
box-shadow: inset 3px 3px 0 rgba(0,0,0,.06);
outline: none;
transition: border-color .15s;
}
.comic-textarea:focus { border-color: var(--blue); }
.comic-textarea::placeholder { color: #aaa; font-style: italic; }
.comic-textarea[readonly] { background: var(--paper2); cursor: default; }
/* SECTION LABEL */
.section-label { font-family: 'Bangers', cursive; font-size: .95rem; letter-spacing: 1px; color: var(--ink); margin-bottom: 6px; text-transform: uppercase; }
/* BUTTONS */
.btn-row { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 14px; }
.btn { font-family: 'Bangers', cursive; font-size: 1.1rem; letter-spacing: 1px; border: 3px solid var(--ink); border-radius: 6px; padding: 8px 20px; cursor: pointer; box-shadow: 4px 4px 0 var(--ink); transition: transform .1s, box-shadow .1s; text-transform: uppercase; }
.btn:active { transform: translate(2px,2px); box-shadow: 2px 2px 0 var(--ink); }
.btn-primary { background: var(--blue); color: #fff; }
.btn-danger { background: var(--red); color: #fff; }
.btn-neutral { background: var(--paper2); color: var(--ink); }
/* ERROR BUBBLE */
.error-bubble {
display: none; position: relative;
background: #fff0f0; border: 3px solid var(--red); border-radius: 14px;
padding: 10px 14px; margin-top: 12px; font-size: .9rem; font-weight: 700; color: var(--red);
}
.error-bubble::before { content: ''; position: absolute; top: -16px; left: 22px; border-width: 0 10px 16px; border-style: solid; border-color: transparent transparent var(--red); }
.error-bubble::after { content: ''; position: absolute; top: -11px; left: 24px; border-width: 0 8px 12px; border-style: solid; border-color: transparent transparent #fff0f0; }
.error-bubble.show { display: block; }
/* OUTPUT COPY WRAP */
.output-wrap { position: relative; }
.copy-btn {
position: absolute; top: 8px; right: 8px;
font-family: 'Bangers', cursive; font-size: .95rem; letter-spacing: 1px;
background: var(--ink); color: var(--yellow);
border: 2px solid var(--ink); border-radius: 4px;
padding: 3px 10px; cursor: pointer;
box-shadow: 2px 2px 0 rgba(0,0,0,.4);
transition: transform .1s, box-shadow .1s;
}
.copy-btn:active { transform: translate(1px,1px); box-shadow: 1px 1px 0 rgba(0,0,0,.4); }
/* SECTION HEADER (colored) */
.section-header {
font-family: 'Bangers', cursive; font-size: 1rem; letter-spacing: 1px;
padding: 4px 10px; border-radius: 4px; border: 2px solid var(--ink);
display: inline-block; margin-bottom: 8px;
box-shadow: 2px 2px 0 var(--ink);
}
/* DIVIDER */
.divider { border: none; border-top: 3px solid var(--ink); margin: 16px 0; }
/* HOW-IT-WORKS */
.how-steps { display: flex; flex-direction: column; gap: 10px; }
.how-step { display: flex; align-items: flex-start; gap: 12px; }
.step-dot { width: 28px; height: 28px; border-radius: 50%; border: 3px solid var(--ink); display: flex; align-items: center; justify-content: center; font-family: 'Bangers', cursive; font-size: 1rem; color: #fff; flex-shrink: 0; box-shadow: 2px 2px 0 var(--ink); }
.how-step p { font-size: .88rem; line-height: 1.5; padding-top: 2px; }
.how-step code { font-family: 'Space Mono', monospace; font-size: .75rem; background: var(--ink); color: var(--yellow); padding: 1px 5px; border-radius: 3px; }
/* STRUCTURE BOX */
.structure-box { font-family: 'Space Mono', monospace; font-size: .82rem; background: var(--ink); color: var(--paper); border-radius: 6px; padding: 12px 14px; margin: 10px 0; }
/* MOBILE */
@media (max-width: 760px) {
.hero { flex-direction: column; gap: 10px; }
.hero-text h1 { font-size: 2rem; }
.info-grid { grid-template-columns: 1fr; }
}
</style>
</head>
<body>
<div class="paper-overlay"></div>
<div data-masthead></div>
<div class="page-wrap">
<div data-tool-hero
data-title="JWT Decoder"
data-chapter="29"
data-category="Encoders & Decoders"
data-icon="🔑"
data-desc="Crack open any JSON Web Token and expose its secrets! View the header, payload, and signature — all client-side, no server snooping."
data-color="green"
data-badges="CLIENT-SIDE,NO SERVER,FREE,3 PARTS,INSTANT"
data-badge-colors="blue,green,yellow,purple,orange">
</div>
<!-- MASTHEAD -->
<!-- HERO -->
<!-- INPUT PANEL -->
<div class="panel">
<div class="panel-header">
📥 PASTE YOUR JWT TOKEN
<span class="panel-tag">INPUT</span>
</div>
<div class="panel-body">
<div class="section-label">JWT Token</div>
<textarea id="jwt-input" class="comic-textarea" rows="5"
placeholder="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"></textarea>
<div class="btn-row">
<button id="decode-btn" class="btn btn-primary">⚡ Decode JWT!</button>
<button id="clear-btn" class="btn btn-danger">🗑 Clear</button>
</div>
<div id="error-bubble" class="error-bubble">
💥 <span id="error-msg">Invalid JWT!</span>
</div>
</div>
</div>
<!-- RESULTS PANEL -->
<div class="panel" id="results-panel" style="display:none;">
<div class="panel-header">
🔍 DECODED RESULTS
<span class="panel-tag">OUTPUT</span>
</div>
<div class="panel-body">
<!-- Token Info Chips -->
<div class="info-grid">
<div class="info-chip">
<div class="info-chip-label">Algorithm</div>
<div class="info-chip-value" id="info-alg" style="color:var(--blue);">—</div>
</div>
<div class="info-chip">
<div class="info-chip-label">Type</div>
<div class="info-chip-value" id="info-type" style="color:var(--purple);">—</div>
</div>
<div class="info-chip">
<div class="info-chip-label">Expires</div>
<div class="info-chip-value" id="info-exp" style="color:var(--orange);">—</div>
</div>
</div>
<!-- Token Color Display -->
<div class="section-label">Token Parts (color-coded)</div>
<div class="token-display" id="token-display"></div>
<hr class="divider">
<!-- Header -->
<div class="section-header" style="background:var(--green);color:#fff;">📜 HEADER</div>
<div class="output-wrap">
<textarea id="header-output" class="comic-textarea" rows="5" readonly></textarea>
<button class="copy-btn" data-target="header-output">📋 COPY</button>
</div>
<hr class="divider">
<!-- Payload -->
<div class="section-header" style="background:var(--purple);color:#fff;">📦 PAYLOAD</div>
<div class="output-wrap">
<textarea id="payload-output" class="comic-textarea" rows="8" readonly></textarea>
<button class="copy-btn" data-target="payload-output">📋 COPY</button>
</div>
<hr class="divider">
<!-- Signature -->
<div class="section-header" style="background:var(--orange);color:#fff;">✍ SIGNATURE</div>
<div class="output-wrap">
<textarea id="signature-output" class="comic-textarea" rows="3" readonly></textarea>
<button class="copy-btn" data-target="signature-output">📋 COPY</button>
</div>
</div>
</div>
<!-- STRUCTURE PANEL -->
<div class="panel">
<div class="panel-header">
🧠 JWT STRUCTURE EXPLAINED
<span class="panel-tag">EXPLAINER</span>
</div>
<div class="panel-body">
<div class="structure-box">
<span style="color:var(--green);">header</span>.<span style="color:var(--purple);">payload</span>.<span style="color:var(--orange);">signature</span>
</div>
<div class="how-steps">
<div class="how-step">
<div class="step-dot" style="background:var(--green);">1</div>
<p><strong>Header</strong> contains metadata — the algorithm (<code>alg</code>) used to sign the token and the token type (<code>typ</code>).</p>
</div>
<div class="how-step">
<div class="step-dot" style="background:var(--purple);">2</div>
<p><strong>Payload</strong> contains the claims — user data like <code>sub</code> (subject), <code>iat</code> (issued at), <code>exp</code> (expiration), and any custom fields.</p>
</div>
<div class="how-step">
<div class="step-dot" style="background:var(--orange);">3</div>
<p><strong>Signature</strong> is generated by signing <code>base64(header).base64(payload)</code> with a secret key. This verifies the token hasn't been tampered with.</p>
</div>
<div class="how-step">
<div class="step-dot" style="background:var(--red);">!</div>
<p>This tool decodes the header and payload client-side. <strong>Signature verification requires the secret key</strong> — never share it!</p>
</div>
</div>
</div>
</div>
</div><!-- /page-wrap -->
<script>
(function() {
var jwtInput = document.getElementById('jwt-input');
var decodeBtn = document.getElementById('decode-btn');
var clearBtn = document.getElementById('clear-btn');
var resultsPanel = document.getElementById('results-panel');
var errBubble = document.getElementById('error-bubble');
var errMsg = document.getElementById('error-msg');
var infoAlg = document.getElementById('info-alg');
var infoType = document.getElementById('info-type');
var infoExp = document.getElementById('info-exp');
var tokenDisplay = document.getElementById('token-display');
var headerOutput = document.getElementById('header-output');
var payloadOutput = document.getElementById('payload-output');
var signatureOutput= document.getElementById('signature-output');
function showError(msg) { errMsg.textContent = msg; errBubble.classList.add('show'); }
function hideError() { errBubble.classList.remove('show'); }
function decodeJWT(token) {
token = token.trim();
var parts = token.split('.');
if (parts.length !== 3) throw new Error('Invalid JWT format. JWT must have 3 parts separated by dots.');
var headerPart = parts[0];
var payloadPart = parts[1];
var signaturePart = parts[2];
try {
var header = JSON.parse(atob(headerPart.replace(/-/g, '+').replace(/_/g, '/')));
var payload = JSON.parse(atob(payloadPart.replace(/-/g, '+').replace(/_/g, '/')));
return { header: header, payload: payload, signature: signaturePart, parts: parts };
} catch (e) {
throw new Error('Failed to decode JWT. Please check if the token is valid.');
}
}
function displayResults(decoded) {
// Info chips
infoAlg.textContent = decoded.header.alg || 'Unknown';
infoType.textContent = decoded.header.typ || 'JWT';
if (decoded.payload.exp) {
var expDate = new Date(decoded.payload.exp * 1000);
var isExpired = expDate < new Date();
infoExp.textContent = expDate.toLocaleString() + (isExpired ? ' (Expired)' : ' (Valid)');
infoExp.style.color = isExpired ? 'var(--red)' : 'var(--green)';
} else {
infoExp.textContent = 'No expiration';
infoExp.style.color = 'var(--ink)';
}
// Color-coded token display
tokenDisplay.innerHTML =
'<span class="token-header-part">' + decoded.parts[0] + '</span>' +
'<span style="color:var(--ink);">.</span>' +
'<span class="token-payload-part">' + decoded.parts[1] + '</span>' +
'<span style="color:var(--ink);">.</span>' +
'<span class="token-sig-part">' + decoded.parts[2] + '</span>';
headerOutput.value = JSON.stringify(decoded.header, null, 2);
payloadOutput.value = JSON.stringify(decoded.payload, null, 2);
signatureOutput.value = decoded.signature;
resultsPanel.style.display = 'block';
hideError();
}
decodeBtn.addEventListener('click', function() {
var token = jwtInput.value.trim();
if (!token) { showError('Please enter a JWT token!'); return; }
try {
var decoded = decodeJWT(token);
displayResults(decoded);
} catch (e) {
showError(e.message);
resultsPanel.style.display = 'none';
}
});
clearBtn.addEventListener('click', function() {
jwtInput.value = '';
resultsPanel.style.display = 'none';
hideError();
});
// Copy buttons
var copyBtns = document.querySelectorAll('.copy-btn');
for (var i = 0; i < copyBtns.length; i++) {
copyBtns[i].addEventListener('click', function() {
var targetId = this.getAttribute('data-target');
var targetEl = document.getElementById(targetId);
if (!targetEl) return;
targetEl.select();
try { document.execCommand('copy'); } catch(e) {}
if (navigator.clipboard) navigator.clipboard.writeText(targetEl.value).catch(function(){});
var btn = this;
var orig = btn.textContent;
btn.textContent = '✔ COPIED!';
btn.style.background = 'var(--green)';
setTimeout(function() { btn.textContent = orig; btn.style.background = 'var(--ink)'; }, 1800);
});
}
// Keyboard shortcut
jwtInput.addEventListener('keydown', function(e) {
if ((e.ctrlKey || e.metaKey) && e.key === 'Enter') { decodeBtn.click(); }
});
// Preload example JWT
jwtInput.value = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyLCJleHAiOjE1MTYyNDI2MjJ9.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c';
})();
</script>
<script src="masthead.js"></script>
<script src="hero-banner.js"></script>
<script src="author-card.js"></script>
</body>
</html>