Sidelong

Sidelong is a writing tool that combines a personal research library with an AI assistant that actually knows what you've saved. Instead of juggling bookmarks, highlights, and notes across a dozen apps, you collect everything — articles, books, YouTube videos, podcasts, tweets — into one searchable library. Sidelong automatically summarizes each save and pulls out key insights. When you start writing in the built-in editor, relevant sources appear beside your draft. You can cite them with one click. The AI chat feature, Ask Sidelong, answers questions using only your saved material and shows you exactly where each claim came from. There's also a deep research mode: type a topic, keep writing, and minutes later a fully cited report lands in your library.

What makes Sidelong different is that it treats your own collection as the source of truth. The AI doesn't guess or make things up — it pulls from what you've actually read and saved. The library accepts imports from Kindle highlights and a Chrome extension lets you save from any page. Every saved item gets a summary and key insights automatically. The editor is clean and distraction-free, with grammar and flow aids. The Ask Sidelong chat can brainstorm angles, find evidence for your argument, or give honest feedback on drafts. The deep research feature produces organized reports with every claim cited, and you can save those sources back into your library.

Sidelong is built for anyone who reads a lot and writes regularly — bloggers, journalists, students, researchers, newsletter writers, and content creators. If you've ever finished a book and forgotten the argument a week later, or spent hours hunting for a quote you know you saved somewhere, this tool solves that. It's especially useful for long-form writing where you need to weave in multiple sources. The free tier gives you the editor and basic features; paid plans unlock more storage and advanced AI capabilities.