Glyphviewer is a web application that analyses web font files. This app will parse any web font file provided as input, and will display its general information (such as name and copyright details) to the user. Glyphviewer also provides a testbed where users can enter text, and have it displayed using the font. Finally, this application can display the characters supported by the font along with their Unicode codepoints.
For more information about this application, see the documentation.
Note: most modern fonts represents hundreds, if not thousands, of characters. When the Shows characters in fonts checkbox is checked, the app will try to display all of the them. The result will be a very long page, which may be an issue for users with bandwidth problems.
This shows information for the font file OpenSans-ExtraBoldItalic-webfont.woff derived from its header.
Here is a sample message. Below it lies a text area where you can enter your test text. Adjust the font size, and click "Try it" to change the message. Hit "Reset" to return all settings to their defaults.