Lettertrace is an open-source, bring-your-own-key tool that tracks how often AI assistants such as Claude, ChatGPT, and Gemini mention your brand across auto-generated prompt variations. It measures visibility, share of voice, prominence, and sentiment per topic, per model, and over time. Users can benchmark competitors, schedule automated monitoring runs, and self-host the entire stack using their own Supabase instance. The MIT-licensed CLI and web app are built for AEO and GEO teams who want full data ownership with no vendor lock-in.