What it does
Manuscript attestation
The strongest evidence that your manuscript was not written by AI.
What it records
Every save adds a record of how text entered the manuscript: typed, pasted, imported, or adopted from another project. The records are linked using a cryptographic hash, so an earlier entry can’t be changed without breaking the chain. Every change you make, from beginning to end, is included in the chain.
From time to time, the chain is sent to a third-party timestamping service (using hash values only), to provide evidence that it existed at a certain point in time. The result is a certificate that can prove the genesis of your manuscript followed the pattern of a human author working on a writing project over time, and not just generated text pasted in from an AI chat.
Attestation requires a $6/month subscription for use of our certificate services, which includes sync functionality. ($10/month after promotion ends.)
What it doesn’t claim
Attestation is completely objective. It reports facts about how the manuscript was written, such as how it was typed, when it was created, and how many changes it went through. It works with every kind of change that Hippocampus supports, including import and sync.
Attestation is not an AI detector, and doesn’t analyze your writing or typing for patterns, so it never gives a false positive. Nor is it a watermark, so it can’t be defeated by any AI model. Finally, attestation doesn’t use AI in any way, so your manuscript is never sent off your computer in plaintext.
Tamper-evident by design
Attestation is designed so that any attempt to change the chained history will be easy to detect and very hard to hide. It uses the same cryptographic technology that secures blockchains in cryptocurrencies like Bitcoin.
For additional security, attestation obtains certificates from third-party timestamp authorities along the way to prove that the state of the manuscript existed as claimed at those points in time. A bad actor who tries to manually type an AI-generated story into an attested manuscript would have to do so over the course of months or years, and also generate a false intermediate history.
Reading & analysis
Knows your book. Answers any question. Tracks every fact. Never writes.
Your most devoted reader
Hippocampus knows your book. Every word you wrote, every piece of research you’ve gathered. Anything you tell Hippocampus to read, it reads, analyzes, and remembers. It all happens automatically, so you never have to keep a character sheet up to date again (unless you want to!).
Since we’re writers too, we’ve come up with features from this reading analysis that actually help with your workflow. Summarize earlier chapters for readers when sending later ones out for critique. Spot continuity issues easily, especially when moving or deleting text. See the structure of your book graphically, based on point-of-view character, location, timeline, narrative thread, and more. Have a question? Ask it, in plain language, and Hippocampus will find the answer in your manuscript. Also, search on a semantic theme or meaning, such as “political intrigue” or “romance,” to automatically list all matching scenes and passages. It’s like having a custom, interactive map to your own book. After using reading analysis features in Hippocampus, it’s hard to go back to keeping manual world-building notes.
Our philosophy
We believe that large language models and other AI tools are able to provide indispensable help to human writers. Now, for the first time in history, computers are able to read and understand prose and poetry, and from that understanding they’re able to build useful support systems for writers. (Programmers have had access to such systems for years now, for the code that they write.) This allows us to bring a whole new class of features that will greatly ease the workload of most writers, so you can focus on your writing.
The tenet we hold, though, is that our tools will never write for you. We believe that art, which encompasses all kinds of human creation, is an expression of the human condition. We don’t have anything against AI-generated writing or media. We just want to focus on human writers.
Technology
If your system supports it, you can run reading analysis directly on your Mac using Ollama, or Core AI on macOS 27, and nothing leaves the machine for ultimate privacy. Local reading analysis requires an Apple silicon computer with at least 16 GB RAM; we recommend 32 GB RAM for the best experience.
You can also choose to use cloud reading analysis, which is available using Anthropic or Google models. Usage is billed à la carte, and doesn’t require a subscription to us or Google or Anthropic. Your privacy is preserved, too, as your plaintext manuscript never touches our servers. It’s sent directly from your computer to the cloud provider, with no account information (other than what the manuscript itself contains). Your writing is never used for training, by anyone.
We are also working with our cloud providers to implement Zero Data Retention (ZDR). This means that they won’t store your manuscript after analysis completes. Without ZDR, such as when using a personal cloud provider account, requests are logged and retained for up to 90 days on their servers. We’ll have specific information about ZDR policies for each cloud provider. Also, ZDR doesn’t apply to materials that violate cloud providers’ terms of service, which apply to all requests sent to them.
Review & feedback
Feedback has never been easier.
Review sessions
Review sessions in Hippocampus are a first-class experience, and a snap to set up and manage. Invite people by email. Choose which chapters to send, and you’re done. Reviewers in a session only see a specific version of your manuscript, so you can continue to work without disrupting them. You can see the session participants, the content, and everything else directly in Hippocampus, without having to wrangle files over email.
When your reviewers reply, their comments appear directly in your manuscript, inline, as you work. Have threaded discussions in comments, and even choose whether reviewers can see and reply to each other’s comments (always, never, or after they’ve submitted their own feedback). Need to add or remove a reviewer? Go ahead. Each reviewer receives a personal encryption key, so only you and they can read the content you sent.
If your manuscript has changed, you can send a new draft to reviewers. You can also browse the draft that reviewers saw exactly as they saw it. See who has submitted feedback, and when, so you can remind stragglers if you want. Done with a session? Close it out, and hide all its comments.
Industrial-strength comments
Hippocampus supports the margin note-style comments that we’re all used to from other writing platforms. Comments are stored in the cloud, end-to-end encrypted, and can take threaded replies from all of the reviewers in a session. Only the reviewers in that session can see each other’s comments, and yours. Each reviewer also has their own encryption key, so you can add or remove them individually from a session. (Reviewers you’ve removed may continue to have access to anything they’ve already downloaded, but cannot see any new review material or comments.)
Professional feedback on a manuscript, such as from a developmental editor, can be very long, even as long as the manuscript itself. Hippocampus is built for these use cases. Reviewers can leave regular inline comments of unlimited length, but also extensive, multi-page notes that come through the review as attachments.
Premium reviewer experience
We think that both writers and reviewers deserve love. Accordingly, we’ve made the reviewer experience as convenient as possible. When you invite reviewers, you only need an email address to send the invitation to. The reviewer receives an email with a button to open the review, with no account or login required. The link in the email contains the reviewer’s encryption key for that session.
Hippocampus for macOS will always be free for readers and reviewers, and reviewers can leave and publish comments from a custom experience in the macOS app.
For reviewers who aren’t on a Mac or who don’t want to download an app, we have a premium reading experience on the web, which has the same beautiful interface, threaded comments, and long-form feedback features that the macOS app has.
Snapshot history
A complete record of your work.
Automatic snapshots
Hippocampus creates snapshots of your work automatically and transparently as you type. You’ll never need to manage your drafts manually again. When you hit an important milestone, star the snapshot (and name it if you want) to refer to it quickly. About to embark on a major rewrite or change your point-of-view character? Drop a star, and have at it.
Your entire snapshot history is contained in your project file, so it’s synced and available on every device. Snapshots are saved with high resolution for the previous two days, so you can go back to almost any point in your typing. Past that, Hippocampus keeps one snapshot a day for the previous month, and then one snapshot a week for the lifetime of the project. Other snapshots are pruned to save space. To preserve a snapshot so it’s never pruned, star the snapshot.
See what changed
You can see exactly what changed in each snapshot, down to the exact word. Read and access content in previous versions of your manuscript at any point in time. You can even browse your whole book at a previous draft in a separate read-only window, for easy comparison with your current draft.
Snapshots tie it all together
Snapshots are the foundation of the Studio in Hippocampus. This is where you manage reviews and exports as well, since these both involve artifacts that are tied to a specific snapshot of your manuscript. Keep all your sharing neat and tidy, with a complete record of which version went to which recipient, and when.
Encrypted sync
Your data is yours, and stays private, even in the cloud
Sync and backup
Sync automatically backs up to the cloud so that your work is safe and accessible from any of your devices. Changes made in one device show up on all devices when Hippocampus is open. All of your data comes along for the ride: your manuscript, research materials, world-building notes, cutting room, and reading analysis.
Sync requires a $6/month subscription, which also includes manuscript attestation. ($10/month after promotion ends.)
Your privacy is a tenet
Your manuscript is end-to-end encrypted with an AES-256-GCM cipher before it is sent to our server. We don’t have a copy of the plaintext, or your 256-bit key, so we can’t decrypt it even if we wanted to. Your key travels with you via iCloud Keychain, and you can back it up using a 24-word passphrase.
We’re committed to your privacy. We encrypt everything we can in your manuscript, including metadata such as reviews, analysis data, and even chapter titles. Materials for review sessions are encrypted before they’re sent to our servers, and we don’t store the keys for these, either. Only you and your reviewers can decrypt them. Furthermore, this doesn’t give reviewers access to your manuscript in general, only the specific chapters and versions you shared with them. When sending materials for cloud reading analysis, the text is sent directly from your computer, and never reaches our server.
Use your own backup solution
Hippocampus files are compatible with all major cloud drive providers, including iCloud, Google Drive, Dropbox, and Microsoft OneDrive. If you prefer to use one of these solutions to sync your work, go ahead. (No Hippocampus subscription required, obviously.) Our file format is engineered to work properly with each of these providers. You can also use a cloud drive as a second backup, so that every file save automatically backs up a complete copy of your manuscript to a location of your choice.
One thing we don’t recommend, though, is using more than one sync method with the same manuscript. For instance, if you’re syncing your book across two computers with iCloud, we recommend not using our own sync service with the same file.
Integrated studio
Best-in-class writing features throughout.
High-performance editor
Hippocampus has a custom editor that’s designed to handle half a million words or more without slowing down. Our editor is written in Swift, so it supports all platform conventions and tools, and behaves exactly as you’d expect a text editor to on macOS. We’ve also included many content creation features, such as Markdown support, tables, lists, images, and even math rendered with LaTeX.
We also innovated with a few editor ideas, including #tags for bookmarks and task tracking, inline comments /* like this */ to make notes to yourself that are never exported or analyzed, and many more. In addition, we integrated tightly with our reading analysis, reviews, and sync features.
We’ve explicitly chosen to focus on content creation and not layout features.
Import and export everything
Hippocampus is here to play well with others in the writing ecosystem. We import your existing documents and projects from all major writing platforms, including Microsoft Word, Google Docs, Scrivener, Ulysses, iA Writer, and common formats such as Markdown and RTF. We import many of these apps’ features as well, including project structure and comments. Furthermore, if you import (or paste) an existing work that consists of many chapters, Hippocampus will automatically offer to structure the chapters optimally for our project format.
We export to Microsoft Word, Markdown, RTF, PDF, plain text, and eBook formats. We support the Shunn manuscript format for quick, reliable submission to editors and agents.
In addition to this, Hippocampus has a native format based on Markdown, so it’s human-readable and diffable. We also export both manuscript and research notes to a Markdown bundle, which preserves your project structure. Your data is yours, and you can take it anywhere you want.
Everything else
Hippocampus is a passion project. We’ve built everything we’ve ever wanted as writers into our app, and we continue to add new things every day. We have a Cutting Room that stores your deleted text, so you can kill your darlings with impunity. Quick navigation to chapters and sections. Find and replace with regular expressions and formatting. A navigator that shows your work by chapter instead of by file. We’re excited about what the future brings.