Twitter (now X) has one of the most comprehensive reservation systems. They block all system terms, verified brand names, celebrity handles (which require verification), common phishing terms, and any username that could be mistaken for an official Twitter account. They also reserve premium short handles for monetization and partnerships.
Instagram follows a similar pattern but emphasizes brand protection more heavily. Given their advertising business, protecting brand names from impersonation is critical. They have dedicated teams reviewing username disputes and a formal trademark claim process for businesses.
GitHub takes a developer-focused approach. They reserve terms that could conflict with the platform — like api, git, help, and status — but are more permissive with personal names and brands. Their focus is preventing technical confusion rather than identity fraud.
Discord reserves gaming and community-specific terms in addition to standard system words. They block terms that could impersonate Discord staff (like discord_admin) and gaming-specific phishing targets. Their approach reflects their user base and the types of scams most common in gaming communities.