MAC Address Validator and Formatter
Check exact MAC syntax, convert formats and inspect bits
Syntax and bit inspection only, up to 1,000 lines / 1 MiB. U/L=0 does not prove registration or worldwide uniqueness. Invalid rows remain visible; copying includes valid values only.
Run the tool or try an example to see results.
About this tool
Inspect one EUI-48 address per line, up to 1,000 records and 1 MiB. Four complete input forms are accepted: six colon-separated byte pairs, six hyphen-separated pairs, three four-digit dotted groups, or twelve plain hexadecimal digits. Mixed separators, spaces inside an address and EUI-64 are rejected instead of being stripped into a different value. Valid rows can be copied in any supported format and letter case. Every row retains its physical source line; invalid values remain visible in the report and are excluded from copied valid values. The first byte supplies the I/G group bit and U/L local bit. Broadcast and all-zero values receive separate labels. These are syntax and bit observations, not proof of worldwide uniqueness, device presence or ownership. No registry lookup or input persistence is used.
Failure Clinic (Common Pitfalls)
A copied subset can look like a complete inventory
Cause: Copy valid values intentionally excludes invalid rows; it does not replace them with guessed corrections.
Fix: Check both counts and the retained physical line numbers. Keep the original inventory until every rejected line has been resolved.
Scenario Recipes
Normalize an inventory without hiding bad rows
Goal: Keep malformed entries visible while producing a usable valid-value list.
- Paste one address per line, retaining blank lines if source line references matter.
- Choose dotted, colon, hyphen or plain output and the desired letter case.
- Run the validator. Fix invalid rows in the original inventory before treating the copied valid subset as complete.
Result: A format-normalized list plus a line-by-line syntax and bit report.
Production Snippets
Accepted spelling and an intentionally rejected mixture
text
00:1B:63:84:45:E6 β 001B.6384.45E6
00-1B-63-84-45-E6 β 001B.6384.45E6
00:1B-63:84:45:E6 β invalid mixed separators
02:42:AC:11:00:02 β local bit 1, group bit 0Frequently Asked Questions
Does U/L=0 mean a globally unique address?
No. It means only that the universal/local bit is zero. A user can type or copy such a value without owning a registry assignment; this tool does not check that assignment.
What happens to invalid lines when I copy?
They remain in the report with their original line numbers and a reason. Copy valid values includes only successfully parsed rows, in source order; compare the valid and invalid counts before using that list.
Are comma-separated addresses accepted?
Use one address per line. A comma, mixed separator or embedded space makes that line invalid. This avoids silently combining malformed inventory fields.
Are all-zero and broadcast values valid device addresses?
They fit the EUI-48 syntax and are labelled as special values. FF:FF:FF:FF:FF:FF is broadcast, while an all-zero value is not evidence of a usable interface assignment.
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