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JWT Inspector

Inspect JWT claims, expiry, issuer and signing algorithm with validation hints.

Best for: Debugging 401s ('is the token expired?'), inspecting what your identity provider puts in tokens, checking clock-skew issues, or learning JWT structure.

Complete guide

Input

How it's calculated & sources
The JWT Inspector uses the standard, deterministic formula, so the same inputs always produce the same result. It runs entirely in your browser, so your inputs are never uploaded. Last reviewed June 2026.

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

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Decode and inspect any JSON Web Token header, payload and signature.

Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is JWT Inspector?
The JWT Inspector decodes a JSON Web Token and shows its header, claims and timestamps in plain language — expiry, issuer, audience, algorithm — with validation hints.
Why does JWT Inspector matter?
You see what the token CLAIMS. Decoding ≠ trusting: only signature verification with the right key proves authenticity — this tool is for reading and debugging, not authenticating.
How is JWT Inspector calculated?
A JWT is three base64url parts (header.payload.signature). The tool decodes the first two locally and interprets standard claims (exp, iat, nbf, iss, aud, sub); it does NOT verify the signature, which requires the signing secret/key.
What are common jwt inspector mistakes?
Treating decoded claims as verified truth — anyone can craft a token; only the signature check authenticates it.
When should you use the JWT Inspector?
Debugging 401s ('is the token expired?'), inspecting what your identity provider puts in tokens, checking clock-skew issues, or learning JWT structure.

What is the JWT Inspector?

The JWT Inspector decodes a JSON Web Token and shows its header, claims and timestamps in plain language — expiry, issuer, audience, algorithm — with validation hints.

How the JWT Inspector works

A JWT is three base64url parts (header.payload.signature). The tool decodes the first two locally and interprets standard claims (exp, iat, nbf, iss, aud, sub); it does NOT verify the signature, which requires the signing secret/key.

  1. Paste the token (from a request header, cookie or log).
  2. Read the decoded header (algorithm, type) and payload claims.
  3. Check the highlighted times: is it expired (exp), not yet valid (nbf), and who issued it (iss)?

Key terms

exp / iat / nbf:
Expiry, issued-at and not-before — Unix timestamps controlling the token's validity window.
alg:
The signing algorithm in the header. 'none' or unexpected algorithms are classic attack red flags.

Common mistakes to avoid

  • Treating decoded claims as verified truth — anyone can craft a token; only the signature check authenticates it.
  • Pasting production tokens of real users into random online tools — this one decodes locally, but the habit is dangerous.
  • Ignoring clock skew when exp 'looks fine' but servers disagree by minutes.

Keywords: jwt, inspect, claims, exp.

Decoded entirely in your browser; the token is never sent anywhere. Decoding does not verify the signature.

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the JWT Inspector free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the JWT Inspector?+

JWT Inspector uses the standard jwt inspector formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The JWT Inspector runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the JWT Inspector on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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Title: I built/used this free jwt inspector — instant, no signup

Body: Inspect JWT claims, expiry, issuer and signing algorithm with validation hints. Try it: https://freetoolsgalaxy.com/tools/jwt-inspector
LinkedIn post
JWT Inspector on Free Tools Galaxy — Inspect JWT claims, expiry, issuer and signing algorithm with validation hints. https://freetoolsgalaxy.com/tools/jwt-inspector
Medium intro
# JWT Inspector — the free tool I keep coming back to

Inspect JWT claims, expiry, issuer and signing algorithm with validation hints.

Try it: https://freetoolsgalaxy.com/tools/jwt-inspector
Quora answer
The fastest way is to use a free in-browser jwt inspector: https://freetoolsgalaxy.com/tools/jwt-inspector. Inspect JWT claims, expiry, issuer and signing algorithm with validation hints.

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<iframe src="https://freetoolsgalaxy.com/tools/jwt-inspector?embed=1" title="JWT Inspector" loading="lazy"
  style="width:100%;height:600px;border:0;border-radius:16px;background:#0b1020"
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<div style="position:relative;padding-bottom:75%;height:0;overflow:hidden;border-radius:16px">
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    style="position:absolute;inset:0;width:100%;height:100%;border:0" allow="clipboard-write"></iframe>
</div>
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Paste in a custom-HTML block or markdown file.
[JWT Inspector — free online tool](https://freetoolsgalaxy.com/tools/jwt-inspector)

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Title
I built a free pregnancy due date calculator that works instantly in the browser — no signup, no ads in your face
Body
Hey r/[subreddit],

I kept needing a quick pregnancy due date calculator and most options online were slow or behind paywalls, so I built one that:

• Runs 100% in your browser (your data never leaves your device)
• No signup, no email wall, no popups
• Loads in under a second on mobile

It covers the standard pregnancy due date use cases (pregnancy, due, date, baby) and links out to the formula + worked examples if you want to learn the math.

Link: https://freetoolsgalaxy.com/tools/pregnancy-due-date-calculator

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