JWT Timestamp Converter
The JWT Timestamp Converter finds the numeric date claims in your token — iat (issued at), exp (expiration) and nbf (not before) — and converts each one from Unix epoch seconds into a readable date and time.
What This Tool Does
JWT timestamps are NumericDate values: seconds since 1 January 1970 (UTC). They are compact for machines but unreadable for humans. This tool decodes the payload, extracts every recognized timestamp claim and renders both the raw value and the converted date so you can reason about a token’s timeline at a glance.
How to Use
- Paste your JWT into the input field.
- See iat, exp and nbf converted to readable dates automatically.
- Compare the raw epoch values with the converted times.
- Copy or download the conversion results.
Key Features
- Converts iat, exp and nbf in one pass
- Shows raw epoch seconds alongside readable dates
- Uses your local timezone for display
- Handles tokens with missing timestamp claims gracefully
- Copy, download and reset actions
- Fully client-side — no data leaves your device
Common Use Cases
- Reading when a token was issued and when it expires
- Debugging clock-skew problems between services
- Checking nbf for tokens that activate in the future
- Verifying issuer lifetime configuration
- Teaching how NumericDate works in JWTs
NumericDate and Clock Skew
RFC 7519 expresses dates as seconds since the Unix epoch, ignoring leap seconds. Because issuers and verifiers run on different clocks, many libraries allow a small leeway (often 30–60 seconds) when evaluating exp and nbf.
If a token seems expired "a little early" or valid "a little late", clock skew between machines is the usual suspect.
Frequently Asked Questions
Which claims does the converter handle?
The three registered timestamp claims: iat (issued at), exp (expiration time) and nbf (not before).
Are JWT timestamps in seconds or milliseconds?
Seconds since the Unix epoch. A millisecond value would produce a date far in the future — a common bug when generating tokens.
What timezone are the converted dates shown in?
Your device’s local timezone. The underlying epoch value is timezone-independent.
What if a claim is missing?
The tool reports only the timestamps present in the token; missing claims are simply omitted.
What is the nbf claim for?
nbf marks the time before which the token must not be accepted — useful for tokens issued now but valid only from a future moment.
Is the token sent to a server for conversion?
No. Conversion is pure arithmetic done locally in your browser.
Related JWT Tools
- JWT Expiry Checker — Check if JWT token is expired and view time remaining
- JWT Lifetime Calculator — Calculate JWT token lifetime duration
- JWT Inspector — Comprehensive analysis of JWT token structure and claims
- JWT Decoder — Decode JWT tokens to view header and payload