Donald Norman’s excellent book The Design of Everyday Things has some great ideas on design in general. I first read it 20 years ago — I’ve been re-reading it recently and it’s still a fun and relevant read. His wish list in the book includes prescient descriptions of the World Wide Web and the iPhone, amongst other things. But the thing that struck me was some very sensible and solid advice on error handling. It’s good advice whether you’re building a coffee maker or a web application.

If an error is possible. someone will make it. The designer must assume that all possible errors will occur and design so as to minimize the chance of the error in the first place, or its effects once it gets made. Errors should be easy to detect, they should have minimal consequences, and, if possible. their effects should be reversible.

He elaborates later in the book:

Design for Error
Assume that any error that can be made will be made. Plan for it. Think of each action by the user as an attempt to step in the right direction; an error is simply an action that is incompletely or improperly specified. Think of the action as part of a natural, constructive dialog between user and system. Try to support, not fight, the user’s responses. Allow the user to recover from errors, to know what was done and what happened, and to reverse any unwanted outcome. Make it easy to reverese operations; make it hard to do irreversible actions. Design explorable systems. Exploit forcing functions.

Norman’s website has a lot of good reading too. His page In Praise of Good Design describes a nice goal to aim for in your web applications:

Eliminate error messages from your system. Always turn an error into an opportunity to help.

I really like the idea of treating an error as part of a natural dialog, a result of the user exploring the system. This makes it much easier to write helpful error messages. But more than this, I think this attitude will help you design more usable applications.

Tags: books, design, errors, usability