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TrackBack: What is TrackBack?

Spammers appear to have discovered TrackBack in a more significant way today. Discussion on the Moveable Type professional developers mailing list is full of folks monitoring how trackback spam is growing and how to stop it. I’m going to post my thoughts on that issue, but thought I should explain trackback first.

What is TrackBack?

If Google is any indication, TrackBack is something that bloggers like to explain to each other a lot. Bloggers also like to refer new users to Movable Type’s documentation, which is intensely detailed and MT-specific, and frankly a little hard to get through. So, perhaps you’ll allow me to take a stab at it:

It’s a three-part technology, and when all three parts work together, it’s a method of automatically notifying other blogs that you’re linking to them. The whole process is something like this:

1) I write a post and link to you.

2) My software tells your software what I did

3) Your software lists my new post on your page.

It’s that simple.  Now, let’s look at the three parts a little more closely.

Part 1: TrackBack Autodiscovery

This is a chunk of code that you put on a Web page (if you use the default templates, it’s there, take a look) that specifies, in an XML computer-y way, how anyone can access your site’s TrackBack system.  When I include links to you in one of my blog posts, my blog software fetches the content of those links for hints about TrackBack URLs.  This, incidently, is why publishing a blog posting that has a bunch of links in it, takes a long time.  Your software is examining all those pages to see if there are TrackBack URLs it should be doing something about.

Think of it this way: Autodiscovery is like putting your snail mail address on your site in a way that your clients address book can automatically sniff out.  That would be pretty handy, wouldn’t it? (Actually, that would be really handy. Would someone go do that, please!)

Part 2: TrackBack Ping

OK, so regardless of whether your software discovers the proper URL, often you can go to the page yourself and there’ll be a little text there that says “The TrackBack URL for this entry is..."  You can enter this in your blog post entry in the field that says “Pings.”

Personally, I think this is why most people don’t understand what TrackBack is.  A TrackBack URL is primarily a notification URL for the other blog, not a URL that delivers information to you, the site’s reader.  This is the opposite of how most URLs that you’re familiar with work.  Programmers don’t blink twice at URLs that require data from you, but regular Web users think of URLs as things that you type into Netscape or Safari, and in this case, it’s a different beast.

A TrackBack ping is a message sent by YOUR blog software to someone else’s blog software, via the TrackBack URL.  Your software is sending details about your post: its title, its summary, its URL, stuff like that.  The other site then stores that information and says “Thanks!” (or maybe “Error!” but we won’t go there).  The ping is complete.

Part 3: The Result

Now what?  Most people allow trackbacks because they want to display, on their own page, the list of people who have “pinged” them.  But strictly speaking, this isn’t covered in trackback.  This is more of a “I’ve got some data that’s interesting, when and how should my software display it” question.  Most people list the trackbacks they’ve received below their comments, and when a new ping arrives, their post pages are rebuilt.  I personally think talkbacks are a little more important than comments and should go first; ultimately, though, you might choose just to look at them yourself on a private page, or through your blog’s admin interface.

In theory, this system, and the resulting display of who’s pinging who, makes the blogosphere a more closely knit, up-to-date, egalitarian place.  Because if I write a post that debunks you, and you allow trackbacks, people reading your post will see that I’m refuting you.  Transparency, truth seeking, openness, etc.

However, spammers may change that… check out the next post.

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