ReaderRead PDFs and EPUBs, look up selected text, and keep your place in a reading library. Add files from your computer or open a book by its URL.
SourcesDefiner supports a wide range of sources including popular dictionaries, translation services, and AI providers. You can also create your own custom sources.
AI SourceConnect to AI providers like OpenAI, Anthropic, Google, xAI, Open Router, and local ones like Ollama and LM Studio. Create custom prompts for everything.
Custom SourceCreate custom sources using URL templates to integrate any online dictionary. Style them with CSS to match Definer's look and feel. Browse examples.
BubbleCustomize when and how the definition bubble appears, adjust its size, and configure activation methods to suit your workflow.
Extension WindowClick the toolbar icon to perform manual lookups using your keyboard as an alternative to selecting text on a page.
ThemesChoose from built-in themes or create your own using the Theme Editor to match your personal style and preferences.
LanguagesChoose the language used by Definer's interface and build an ordered list for lookup results. Decide whether Definer follows the list or remembers your choices.