diff --git a/doc/DESCRIPTION.md b/doc/DESCRIPTION.md
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-Some long and extensive description of what the app is and does, lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
+# TrustyHash - A Trustable Hash Calculator
 
-### Features
+TrustyHash is a small [client-side](https://unhosted.org/) web application that
+computes SHA-256 hash values on both local files and on remote URLs, with a
+strong emphasis on a process that will allow you to trust the results. Works
+offline!
 
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+TrustyHash homepage: https://github.com/sprin/TrustyHash
+
+[Use it here](https://sprin.github.io/TrustyHash/)
+
+## How is this useful?
+
+Integrity: "We have in hand the same set of sequences of bits that came into
+existence when the object was created" - [Lynch](http://www.clir.org/pubs/reports/pub92/lynch.html)
+
+"Friends don't let friends use unverified downloads."
+
+This fills a need for a verifiable, web-based hash calculator written in free
+JavaScript. If you already use the command-line hash utilities on your
+system, you should continue to use those. This is targeted towards users who do
+not have or are unable to use the hash utilities on their local systems. While
+universal command-line-literacy is a good goal, the concepts of file integrity and
+authenticity and the ability to use tools for verification are perhaps more
+fundamental.
+
+Integrity is the first link in secure systems, and key to determining
+authenticity. If we trust the association between an author and the hash value
+of a file they created, perhaps because we trust them and they gave us the
+hash in person, we can authenticate whether a file we believe to be the same
+really did come from them. We can achieve the same result if the author had
+used a signing key, and signed and distributed a hash value along with the
+file, and we could trust the association between a particular key and the
+author - albeit with somewhat more complexity and caveats (eg, has the signing
+key been kept private?).
+
+In a few words, this tool aims to enable verification of integrity and
+authenticity claims in an accessible way that depends only on a trusted hash
+value and the correctness and integrity of the TrustyHash app and the browser
+it executes in. See the section "Trust" below for recommendations on
+how to verify integrity of this application.
+
+## Usage
+
+Local files can be opened from a file select dialog, or dragged into the "drop
+area". Remote URLs can be entered, and if the remote server allows cross-origin
+GET requests via
+[CORS](https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS),
+the file will be downloaded to the browser, with the option of saving locally.
+
+It's recommended to save the application, verify the integrity, and use the
+saved copy from then on. To save from the browser, use "Save Page" > "Web Page,
+HTML Only", and use a filename of `TrustyHash.html`. To verify, read the
+section on "Trust" below.