A reading library on your own computer.

Save articles and PDFs, read a clean copy, and keep highlights and notes beside the text. The sponge command captures on your Mac or Linux computer. An optional account syncs the text to your browser, your Mac, and your iPhone.

Get started Sign in or create an account Download for Mac

Capture needs one computer running sponge, with Node.js 24.20 or newer. Links saved from other devices wait in a queue until it captures them. How Sponge works.

The Sponge web library with an article, a summary, and a highlighted passage. — The web library itself, running in this page over eight pieces from a real library, each shown as a short summary that links to its source. Open one, press `⌘K` to search, select a passage to highlight it. Nothing is saved or sent.The web library, shown with pieces from a real library.

In the library

Read and organize: An inbox, a read-later queue, and an archive, with stars, reading progress, and a key for each. Sort by newest, oldest, shortest, or longest.
Reader: A clean copy with an outline, tables, footnotes, highlighted code, and math. Choose a dark, light, or sepia theme, sans or serif text, and the text size, spacing, and width.
Highlights and notes: Select text to highlight it or comment on it, and add notes about the whole piece. A notebook collects every highlight and note across the library. Search it, then copy or download it as Markdown.
Search: Search by keyword or by meaning, across the library and inside the open article. Filters such as is:starred kind:pdf or site:example.com narrow keyword results. Both kinds of search run in your browser, on its own copy of the library.
Related reading: The end of an article names up to three other saves closest to it in meaning. The comparison runs in your browser.
Summaries you review: A model on your computer drafts a summary with verbatim quotes. Nothing shows until you accept it, from the terminal. Summaries need a model download.
Library map: A map of the concepts that several saved articles share, built from the summaries you accepted. Any browser can view it; building it needs an Apple Silicon Mac.
Offline: Once loaded, the library reads and searches without a connection. Changes made offline are sent when you are back online. On a computer that holds the library, sponge open shows it in any browser with no connection and no account.
Sharing: Everything starts private. Share an unlisted link, or publish chosen items to a public page with feeds. Others see the title, the source link, and the summary you accepted, never the saved text or your notes.

The web library in detail.

The highlights notebook in the Sponge web library, listing highlighted passages and notes from four articles with an Export button. — The highlights notebook, shown with sample highlights on real reading.

Ways to save

Terminal: sponge add URL --wait captures a page or a PDF now.
Web library: Save a link from the library in any browser, including on a phone.
Mac: The Mac app saves from the Share menu, the menu bar, a keyboard shortcut, or the Dock.
Chrome: Sponge for Chrome saves the tab you are reading from the toolbar, a right-click, or Alt+Shift+S.
iPhone and iPad: The iPhone and iPad app opens your library and adds Sponge to the Share sheet.
Coding agent: With sponge mcp connected, an agent captures a page now or adds a link to your queue.
Your own tool: The Clip API queues links. A clip token can queue saves but cannot read the library.

Every way to save, and how the queue works.

In the terminal and with agents

Commands: sponge list, sponge show, sponge search, and sponge comment read and annotate the same library. Add --json to any command for structured output. CLI reference.
Ask your library: sponge ask answers a question from what you have saved, in a few short statements. Each statement is shown with a quote, and only when that quote is found in the item it cites. It uses the same local model as summaries. How an answer is made, and its limits.
Coding agents: Claude Code, Codex, OpenCode, and other agents search, read, save, and annotate through the CLI or MCP server. The find_passages tool returns the paragraphs that bear on a question, each with its item and its page or time.

$ sponge ask "what temperature should green tea be steeped at?"

Green tea is steeped at about eighty degrees, cooler than black tea. [1]
The lower temperature keeps the leaves from turning bitter. [1]

[1] Tea notes
    0a57a26ade13…
    “Green tea is steeped at a lower temperature than black tea, usually around eighty degrees”
    “so the leaves do not turn bitter”

An illustration with invented reading, not a captured run.

Where it lives

On your computer: The library is a SQLite database and files on your disk. It works without an account.
In the cloud, if you sync: Text only: saved articles, highlights, and notes. PDF files stay on the devices that hold them, and images load from the sites that published them. Cloud copies are protected by TLS and the storage provider, and are not end-to-end encrypted.
Capture and models: Both run on your computer. Nothing you save is sent to an AI service.

Media transcripts, terminal semantic search, and building the library map need an Apple Silicon Mac with macOS 26. Requirements and platforms.

Plans

Free: An unlimited local library, with cloud sync for up to 100 saved items.
Sponge Plus · $5 / month: Unlimited saved items in the cloud. Get Plus.

At the limit, your library stays readable and exportable. Plan details and questions.