What is SSML?

Markup solves the problems plain text cannot express. A pause of exactly half a second, a phone number read in digit groups, a name spelled phonetically.

Numbers and dates are the common reason people reach for it. The string 1/2 could be a date, a fraction or part of an address.

Support varies between engines, which is the practical annoyance. Markup that works in one system is ignored in another.

It is a fix for specific lines rather than a way to write a whole script. Most sentences do better as plain, short, spoken English.

The clearest case for it is a line that has to be right every time, such as a clinic address containing a street name the engine keeps mispronouncing.

Say your clinic sits at 1204 Goethe Street and the phone number is 312 555 0142. Given plain text, an engine might say "one thousand two hundred four Goath Street". It might then run your phone number together as a single huge figure. Every caller who needs directions hears that mistake.

Markup fixes each part with its own tag. A substitution tag swaps in "twelve oh four" wherever your script says 1204. For the street name, a phoneme tag spells out the sounds, roughly "GUR-tuh". Next, a say-as tag marked as telephone reads the number digit by digit. Add a break tag of 300 milliseconds after the area code, and your caller has time to write the first three digits down before the rest arrive. That's four small edits on two lines, and the rest of your script stays plain English.

Markup pays off when a line is said on nearly every call and has to be right each time. Your address, your phone number and a doctor's surname all fit that test. For anything said once a week, it isn't worth your afternoon.

Try the cheap fix first. Writing "Gurta Street" in your script often works as well as a phoneme tag, and you can test it in a minute by calling your own line. Spelling a number out as words does the same job for a price or a suite number.

If you're comparing vendors that do accept markup, ask which tags their engine honors. The W3C standard is long and most engines support only part of it. A say-as value that works in one product can be read aloud as literal text in another. Ask for their supported tag list in writing, then test your one hard line against it before you sign.

GreetKeeper is written in plain language rather than markup. You type what the assistant should say.

Where a word is mispronounced, spelling it phonetically in the script is the fix that works without any markup at all.

Numbers and addresses are the cases worth testing before you go live, because they are where reading aloud goes wrong most often.