In Disassembling a SWF with swfdump, Gordon Smith outlines how to use the open source Flex SDK download and its swfdump executable tool based on the provided swfutils.jar. Note that the swfdump executable is also available with the OpenLaszlo distribution in the same directory (WEB-INF/bin) as other Flex-specific commands such as mxmlc and asdoc.
The flash-decompiler project, hosted on Google Code, is intended to be used to decompile Flash files. There are also other Flash decompilers, including commercial products. These include Flash Decompiler, Flash Decompiler Gold, and Sothink SWF Decompiler. Other tools for determining SWF content include swfextract, abcdump, and Flare.
My favorite product for seeing how my Flash/SWF files have been put together is the easy-to-use Nemo 440. This AIR-based application is very simple and therefore very easy to use. It is relatively small in size and so downloads and installs quickly, especially if you already have Adobe AIR installed on your machine. Once the
.airfile is downloaded, it can be installed by clicking on it or by typing its name on the command-line. There are only a few choices once the application is loaded, so it is really easy to figure out how to use Nemo 440.
Looking at the code as available in the SWF can be useful in understanding better how the Flex-to-Flash process works and can be useful for ensuring that contents are being included in the SWF as you expect.
Even if you don't have a need to look at the contents of your SWF file for your own uses, it may be worth your time to look at what Nemo 440 and other similar tools do show from your files. You may find that there are some things in those files that you really don't want so easily observed. See Analyzing Malicious Flash Programs for additional details on such security implications.
For times when you need to peek into an SWF you have compiled, Nemo 440 is an extremely useful tool that makes viewing of this content easy and efficient.