Twelve bars, and almost every one of them a dominant seventh. That last part is what makes this a blues rather than a set of changes that happens to be twelve bars long: in a major key the tonic would be a major seventh and the subdominant would be another, and here they are both dominants, which is a piece of harmonic behaviour that came out of the music rather than out of a system.
What the twelve bars are doing
The first four establish the tonic and take one early trip to the subdominant — the trip that tells a listener within seconds which of the two the tune is going to spend its time on. Bars five and six sit on the subdominant properly, and bar six is the one bar in the form declared as something other than a plain seventh: a diminished seventh a semitone above it, which is how the harmony climbs back rather than simply dropping. Bars seven and eight leave the tonic for a dominant built on the sixth degree, which is not diatonic and is not trying to be — it is there to point at the supertonic that opens bar nine. Bars nine, ten and eleven are the cadence, and bar twelve hands the whole thing back to bar one.
In any key somebody calls
The page opens in F, because a room with a horn in it calls this in F more than anywhere else, and B flat and E flat after that. Click any other key above and the same twelve bars are recomputed — not looked up. The chord symbols are spelled the way a chart spells them, with flats where flats belong, while the links underneath keep the network's own sharp-based addresses, so the page can write B flat and still point at the same page every sister site uses for that pitch.
What the five rules make of it
Below the form you will find each rule run over these bars. The tritone rule has eleven dominants to work with and takes all of them, which is more a demonstration than an arrangement — nobody plays that. The insertion rule finds the seven bars a dominant has to itself. The backdoor rule finds three places where a dominant is resolving up a fourth. The diminished rule finds nothing at all here, and says so, because no two neighbouring chords in this form sit a whole tone apart.