diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -1,2 +1,22 @@
 # spectralyze
 A commandline tool for fourier transforming audio files
+
+## Usage
+```
+spectralyze file1 [file2...]
+```
+
+## What does it do
+Spectralyze reads one or more audio files from the standard arguments and creates JSON files containing the spectrum of the file. 
+Each audio channel in the file is transformed separately. The resulting JSON has the following structure
+```
+{
+  "channel_1": [
+    {"freq": 0.0, "mag": 1.0"},
+    {"freq": 0.1, "mag": 1.1"},
+    ...
+  ],
+  "channel_2": ...
+}
+```
+Every supplied audio file will result in one JSON file. The magnitude is the absolute value of the real and imaginary part of the Fourier transformation.