Lightkone Reading and highlighting
The reader
Open a paper and press Read. The PDF opens full screen, on a phone too. Pinch or use Zoom in / Zoom out, and the moon button turns the pages dark for reading at night. Esc or the close button returns to the list, where Lightkone remembers the paper in Recently read.
No PDF yet? Get free PDF looks for an open copy (arXiv, or Unpaywall with a contact email set under Settings → PDFs). Attach PDF adds a file of your own, and Replace PDF swaps it.
Highlights and notes
Select text on a page, then tap:
- Highlight to mark it;
- Highlight + note to mark it and write a note;
- Explain (with a Claude key) to have Claude explain the passage, or an equation, in the context of the whole paper. It sees the PDF and a picture of what you selected, takes follow-up questions, and can keep its answer as the highlight's note.
- Ask (with a Claude key) to put the passage in the chat beside the page, and ask your own question about it.
Tap a highlight to edit its note or delete it. Highlights are saved in
lightkone/annotations/<paper id>.json next to the library, as plain JSON,
and never inside the PDF, so the file stays as published.
The side panel: notes and chat
The panel button at the top right of the reader opens a side panel beside the pages, with two tabs:
- Notes lists your highlights and their notes. Tap one to go to it; Export as Markdown or Copy takes them all.
- Chat is one running conversation with Claude about the paper you are
reading. It picks up where you left it, on any device: Claude sees the
whole conversation so far with each question. Summarize (in the
paper's details) and Explain on a passage add to the same running chat
instead of starting new ones, and Ask on a selected passage asks in it.
+ starts a separate chat when you want a clean start, which then
becomes the running one; the list at the top switches between the paper's
chats, and the pencil names the chat shown (or the new one, before you
ask). When a chat grows long (20 messages, or about 15,000 tokens of text
sent again with each question), a note above the question box offers a
new chat; Keep going hides it for that chat. Claude reads the whole PDF
with each question. Every chat
is kept with your other chats, under the paper, in
lightkone/history/(in a shared or read-only library, in this browser only). The chat button opens it in Chats, to rename, pin or bring in other papers.
Sources highlighted on the paper
Claude backs each answer with quotes from the PDF: the passages that answer your question and those that help you follow the answer, such as a definition, an assumption, a step or an equation, several when several parts of the paper matter. Each quoted passage is highlighted in blue right on the page, with a numbered marker in the margin beside it, and the answer shows the same numbers with the page, like 2 · p. 3. Tap a number in the answer, or a marker on the page, to go to that passage.
The Sources bar over the page steps through them: ‹ and › go to the previous and next passage, and Back returns to where you were reading before the first jump. × hides the highlights (tapping a number in the answer shows them again). A passage whose words can't be found on the page (rare, for some scanned or unusual PDFs) is counted as "not marked", and its number opens its page instead. The highlights are those of the latest answer in the chat shown, and come back when you reopen the chat; they are not saved as your own highlights. A saved answer keeps its quotes, so it shows the same highlights without asking Claude again.
Numbers in Ask and in Chats that point to a page of a paper open the paper there with the quoted passage highlighted the same way.
On a computer, the three panel buttons next to the close button snap the panel to the right, the left or below the page, and the fourth floats it over the page as a window: drag its tab bar to move it and its bottom-right corner to resize it. Drag its inner edge to make it wider or narrower (taller or shorter below the page), or focus the edge and use the arrow keys; Lightkone remembers the place and the size for each place, and a double-click on the edge goes back to the default size. On a phone the panel is a sheet over the lower half of the screen, so the page stays in view above it; the arrow makes it taller, and it moves up above the keyboard while you type. Lightkone remembers which tab you used last.
The paper's own Notes box (in its details) is for notes on the whole paper. It is searched along with everything else.
Summaries and questions
With a Claude key, a paper's details offer Summarize and Chat about it, which opens a chat about the paper in Chats. Ctrl J (⌘J) does the same while you read. When the PDF is stored, Claude reads the whole paper, not only the abstract. To ask across your whole library, use Ask at the top (see Finding papers).
Export to Obsidian
Export to Obsidian (side bar, Write) writes one Markdown note per paper,
named @<citation key>.md, with the paper's details, your highlights (each
linking back to its page in Lightkone) and your notes. Choose your vault's
folder to write the notes straight into it (Chrome and Edge), or download a
.zip. Run it again later and only the part above the marker line is
rewritten: what you wrote below it in Obsidian is kept.
Reading offline
Lightkone keeps the last 25 PDFs you opened on the device. To choose more, for a flight or a trip, open Offline papers (in the side bar under Organize, or Ctrl/⌘K):
- Pick a folder, tag, Starred or a search first. The panel then offers to keep every paper in that view, and downloads their PDFs, highlights and notes.
- On a single paper, press Keep offline in its details.
- Kept papers show an Offline label in the list. They stay until you remove them, one by one or with Remove all.
- They take space on the device, within a limit you set (500 MB to 10 GB, 2 GB at first). Keeping stops at the limit and says so.
For the app itself to open with no network, install it (Install app or Add to Home Screen) and open it once before you go.
With no network you can read, highlight and take notes. Highlights are kept on the device and saved to your storage when you are back online, even if the app was closed meanwhile. Other changes (notes, stars, folders) are saved when you are back online as long as Lightkone stays open; the top bar says Offline, saves later until then.
This applies to a bucket or a GitHub repository. With This browser only, everything is on the device already.
Saved web pages
A web page added to the library (a blog post, a report, documentation) is saved twice: its raw HTML exactly as it was fetched, and its main text as Markdown, found with Mozilla's Readability, the engine behind Firefox's reader view. Read opens the Markdown as a quiet column of text, with headings, figures, links, tables and math. Saved page shows the HTML as it was saved, in a sandbox where none of the page's scripts run. The moon gives a dark page, and the toolbar copies or downloads the Markdown, ready for Obsidian.
The Markdown is also the page's text for search, Ask and the MCP server, as a PDF's text is. Pages that build their content with scripts after they load may save little text; their raw HTML is kept all the same. Figures stay on the site they came from, so they show only with a network.
Some sites turn away anything that isn't a person's browser, often with a "checking your browser" page. Lightkone then reads the page through Jina Reader (r.jina.ai), which opens it in a real browser; only the page's address goes there, and Settings → DOI, arXiv and BibTeX switches it off. When that fails too, the page is still added, as a link with a title made from its address, and Add papers says why no copy was kept. To keep a copy, open the page in your browser and use the + Lightkone bookmark (set it up once from Add papers; on a phone, tap the address bar, type Lightkone and tap the bookmark): the page as you see it goes to Lightkone and is saved. Or save the page in the browser (in Chrome on a phone, menu, then Download, an .mhtml file; on a computer, Save page as) and use Add files in Add papers, drop the file on Lightkone, or share it to the installed app. The saved page gets the same Markdown copy and reader as a fetched one, and a page already in the library as a link gets the copy.
Reading at night
With the Dullaby plugin set up (Settings → Dullaby night reading), Read at night opens a paper in Dullaby's calm, dim reading mode.
The link that opens Dullaby also carries your library, as identifiers only:
arXiv ids (or DOIs), newest first, marked when starred or never opened. No
titles, authors, notes or PDFs. It travels in the part of the address after
#, which browsers never send to a server, and Dullaby keeps it on that
device. Dullaby then looks for new papers near yours and skips the ones you
already have. Read at night in Dullaby under Discover opens it with the
library and no paper, to bring it up to date.
Papers you Keep in Dullaby come back here: its list of kept papers has Add to Lightkone, which opens this app's Add panel with the paper.