6 min read · Try Unix Timestamp
Seconds or milliseconds?
JavaScript `Date.now()` returns milliseconds; many Linux logs use seconds. A ten-digit value is usually seconds; thirteen digits usually milliseconds. Converting the wrong unit shifts dates by decades.
UTC vs local display
Epoch is UTC by definition, but humans read local time. When correlating logs across regions, convert to UTC first, then to each operator’s zone for incident timelines.
JWT exp and nbf
Token expiry claims are numeric dates in seconds. Compare `exp` to current UTC epoch when debugging “token expired” errors—clock skew between services matters.
Spreadsheet pitfalls
Excel may truncate large integers. Paste epoch values as text or use a dedicated converter instead of letting spreadsheets auto-format scientific notation.
This article is part of the DevToolsHub learning guides—original writing meant to complement our free tools, not replace official documentation from vendors or standards bodies.