Handle Validation

This document defines the validation rules for user handles in Mastic. These rules follow the Mastodon username conventions to ensure compatibility with the broader fediverse.

Local Handle Format

A local handle is the username portion of a Mastic account (e.g. alice in @alice@mastic.social).

Regex: ^[a-z0-9_]{1,30}$

Underscores are allowed in any position, including leading, trailing, and consecutive.

Local handles are intentionally restricted to ASCII. Mastic owns the local namespace and the users.handle column carries a unique index that must remain free of Unicode normalization ambiguity (NFC vs NFD, confusables, IDN homograph). Users on other fediverse instances may have Unicode handles — see the next section.

Remote Handle Format

A remote handle identifies a user on another fediverse instance (e.g. @bob@mastodon.social, @user@ꩰ.com). Remote handles are discovered via WebFinger (RFC 7033) using the acct: URI scheme defined by RFC 7565, where both the userpart and the host are UTF-8.

To remain federation-compatible with Mastodon, Pleroma, Misskey, GoToSocial, and other ActivityPub implementations — many of which allow Unicode usernames and IDN domains — Mastic accepts a broader character set for remote handles.

Userpart

Pattern (PCRE-style): ^[\p{L}\p{N}_.\-]{1,64}$.

Punctuation other than _, ., - is rejected. Whitespace and control characters are rejected.

Host (domain)

The host is treated as an Internationalized Domain Name (IDN). Unicode domains such as ꩰ.com are accepted; for storage and comparison the host is normalized to its ASCII Compatible Encoding (Punycode, UTS #46).

Storage

Remote handles are stored in canonical form <unicode_userpart>@<ace_domain>, with the userpart Unicode-lowercased and the domain in lowercase A-label form. Two handles compare equal iff their canonical forms are byte-equal.

Implementation note. Mastic does not yet perform IDN normalization at runtime; remote handles arriving with Unicode hosts are accepted but stored as received. Punycode normalization will be wired into the federation canister alongside WebFinger lookup (tracked separately).

Reserved Handles

The following handles are reserved and cannot be claimed during sign-up. These match system routes and well-known service names commonly reserved across fediverse implementations.