The Username Format That Works on the Most Sites: We Tested 21 Formats Against 3,457 Sites’ Rules

You found a username you like. Will every site actually let you register it? We took 21 versions of a simple handle, such as johnsmith, john_smith, john.smith and longer or shorter variants, and tested each one against the username rule stored for every site in our engine: 3,457 sites, October 25, 2026.

The short version: letters and digits pass everywhere. Underscores pass almost everywhere. Dots and hyphens each pass on only about 41% of sites. Spaces and accented letters pass nowhere. And length starts to hurt at 21 characters.

Key findings

• Letters and digits are universal. johnsmith and johnsmith92 were accepted by 100% of site rules.
• Underscores are nearly universal. john_smith passed on 99.6%. The exceptions include Bluesky, GitHub and several blog platforms.
• Dots and hyphens split the web. john.smith passed on 40.9% and john-smith on 41.3%.
• 20 characters is the safe ceiling. Acceptance stays at 99.9% up to 20 characters, then drops to 88.4% at 21 and 41.2% at 31.
• No spaces, no accents. A space or a letter like ö passed on 0% of sites.

Which characters work

Underscore variants all behaved the same: starting with an underscore, ending with one and using two in a row each passed on 99.6%. Starting with a digit passed on 99.9%. Capitals passed on 99.7%, though many sites store names in lowercase anyway, so JohnSmith and johnsmith are often the same account.

Dots and hyphens are the real split. Most fediverse software allows underscores but not dots or hyphens, and that software makes up most of our list. If your handle is john.smith, expect to become john_smith or johnsmith on more than half the sites.

How long is too long

The drops line up with the most common maximum lengths. 1,629 sites cap names at 30 characters, 586 at 60, 447 at 50, 396 at 20 and 377 at 40. Short names are rarely a problem by rule: 3,445 sites accept a single character. In practice short names are almost always taken, which our 60-username study showed clearly.

The big platforms with stricter rules

For these major sites our engine stores a site-specific rule. These are the ones most likely to reject a handle that works elsewhere.

• Bluesky: 3 to 18 characters, letters, digits and hyphens. No underscores or dots.
• Discord: 2 to 32 characters, lowercase letters, digits, underscores and dots. No capitals, no hyphens, no two dots in a row.
• GitHub: 1 to 39 characters, letters, digits and hyphens. No underscores or dots.
• Snapchat: 3 to 15 characters starting with a letter. Letters, digits, dots, underscores and hyphens.
• TikTok: 2 to 24 characters, letters, digits, underscores and dots. No hyphens.
• Roblox: 3 to 20 characters, letters, digits and underscores.
• Minecraft Java: 3 to 16 characters, letters, digits and underscores.
• LiveJournal: 1 to 15 characters, lowercase letters, digits and hyphens.
• WordPress.com: 4 to 63 characters, lowercase letters and digits only.
• Blogger, Substack and Gumroad: 1 to 63 characters, lowercase letters, digits and hyphens.
• Bandcamp: 1 to 63 characters, letters, digits and hyphens.
• itch.io: 1 to 63 characters, letters, digits, underscores and hyphens.
• GitLab: 2 to 255 characters.

Notice the conflict. Bluesky and GitHub want hyphens and refuse underscores. TikTok and Discord refuse hyphens. The only separator-free handle that passes all of them is plain letters and digits.

The safest format

Based on these rules, the handle most likely to work everywhere:

• 3 to 15 characters long
• letters and digits only
• starts with a letter
• all lowercase, so it looks the same on sites that lowercase names

If you want a separator, an underscore is the better bet, but plan a plain version for Bluesky, GitHub and blog platforms. Avoid dots and hyphens in your main handle. Stay at 20 characters or fewer, and at 15 or fewer if LiveJournal or Snapchat matters to you. Then check whether the name is free with the name checker or the username search. Our guide to choosing a unique username helps if you need ideas.

How we did this

• Sites: all 3,457 sites in our private engine on October 25, 2026.
• Formats: 21 sample handles built from johnsmith, each changing one thing: a character, the case, the first or last character, or the length (1, 2, 15, 16, 20, 21, 25, 30 and 31 characters).
• Test: each handle was matched against the username pattern and length limits stored for each site. A site counts as accepting a format if its rule allows it.
• Published: only totals and the named major-site rules above. We don't publish per-site rules.

Download the summary data (CSV)

Limitations

• This measures what our engine's rules accept, not what each site's sign-up form accepts. For many big platforms we store a general permissive rule instead of the platform's exact published limits, so we only name the major sites with site-specific rules.
• Most of our list is fediverse servers and forums, so the percentages reflect their rules most of all.
• Sites can reserve names, ban words or change limits at any time. A handle that passes a rule can still be refused at sign-up.
• A format passing a rule says nothing about whether the name is free. That needs a real check.

FAQ

Can I use a dot in my username?

On TikTok, Discord, Snapchat and some others, yes. Across our whole list it passed on only 40.9% of sites, so avoid it if you want one handle everywhere.

Underscore or hyphen?

Underscore. It passed on 99.6% of sites against 41.3% for a hyphen. The exceptions are Bluesky, GitHub and blog platforms, which take hyphens only.

What is the best username length?

3 to 15 characters. That fits every major-site rule above except WordPress.com's 4-character minimum.

Do capitals matter?

Capitals passed on 99.7% of rules, but Discord, WordPress.com and others only allow lowercase. Lowercase is the safe choice.