diff --git a/docs/why.md b/docs/why.md
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--- /dev/null
+++ b/docs/why.md
@@ -0,0 +1,117 @@
+# Why use this API?
+
+[Deutsche Bahn itself provides an API.](https://data.deutschebahn.com/dataset/api-fahrplan) Why use this one? (And what could DB do better?)
+
+## Realtime Data
+
+This API returns realtime data whenever its upstream, the [API for DB's mobile app](https://gist.github.com/derhuerst/2a735268bd82a0a6779633f15dceba33), provides it.
+
+## No API Key
+
+Especially on web sites/apps, it is a subpar solution to the send API keys to the client. Also, you have to obtain these keys manually and cannot automatically revoke them. **This API doesn't require a key.**
+
+## Sane Markup
+
+Compare the official API:
+
+```js
+{
+	cid: 'C-0',
+	date: '20171216',
+	dur: '043200',
+	chg: 2,
+	sDays: { /* … */ },
+	dep: {
+		locX: 0,
+		dPlatfS: '6',
+		dInR: true,
+		dTimeS: '115400',
+		dProgType: 'PROGNOSED',
+		dTZOffset: 60,
+		type: 'N'
+	},
+	arr: {
+		locX: 2,
+		aPlatfS: '4',
+		aOutR: true,
+		aTimeS: '162600',
+		aProgType: 'PROGNOSED',
+		aTZOffset: 60,
+		type: 'N'
+	},
+	/* … */
+}
+```
+
+to this one:
+
+```js
+{
+	origin: {
+		type: 'station',
+		id: '8089066',
+		name: 'Berlin Friedrichstraße (S)',
+		location: {
+			type: 'location',
+			latitude: 52.520331,
+			longitude: 13.386934
+		},
+		products: {
+			nationalExp: false,
+			national: false,
+			regionalExp: false,
+			regional: true,
+			suburban: true,
+			bus: true,
+			ferry: false,
+			subway: true,
+			tram: true,
+			taxi: false
+		}
+	},
+	destination: {
+		type: 'station',
+		id: '8004158',
+		name: 'München-Pasing',
+		location: {
+			type: 'location',
+			latitude: 48.150036,
+			longitude: 11.461624
+		},
+		products: {
+			nationalExp: true,
+			national: true,
+			regionalExp: false,
+			regional: true,
+			suburban: true,
+			bus: true,
+			ferry: false,
+			subway: false,
+			tram: true,
+			taxi: false
+		}
+	},
+	departure: '2017-12-16T11:54:00.000+01:00',
+	arrival: '2017-12-16T16:26:00.000+01:00',
+	price: {
+		amount: 150,
+		hint: null
+	}
+}
+```
+
+## GZIP support
+
+Especially on cellular connections, gzipped responses improve the performance a lot.
+
+## HTTP/2
+
+[HTTP/2](https://http2.github.io/) allows multiple requests at a time, efficiently pipelines sequential requests and compresses headers. See [Cloudflare's HTTP/2 page](https://blog.cloudflare.com/http-2-for-web-developers/).
+
+## More Features
+
+This API enhances the functionality of their API with static data, which is used in e.g. `GET /stations`.
+
+## Monitoring
+
+There's a [status board](https://status.transport.rest) that indicates the health of the API endpoints.
diff --git a/readme.md b/readme.md
index 31be487..d31771b 100644
--- a/readme.md
+++ b/readme.md
@@ -2,7 +2,7 @@
 
 **A clean REST API wrapping around the [Deutsche Bahn](https://en.wikipedia.org/wiki/Deutsche_Bahn) [API](https://github.com/derhuerst/db-hafas#db-hafas).**
 
-[API Documentation](docs/index.md)
+[API Documentation](docs/index.md) | [Why?](docs/why.md)
 
 [![dependency status](https://img.shields.io/david/derhuerst/db-rest.svg)](https://david-dm.org/derhuerst/db-rest)
 ![ISC-licensed](https://img.shields.io/github/license/derhuerst/db-rest.svg)