> when it can't be found by scraping a web page?

This is the very purpose of those tokens! The reason they're like that, is because you won't encounter it in random content, so during training, you can put them where you want them to end up at prediction time.

(this is just made up tokenization but it's close enough to the real world)

If the user types <tool_call>, you get < (token id = 32), tool_call (41), > (102). It never decodes to <tool_call>, which is spicy number 12345, for example.

The tool call tokens are _always_ composed of multiple real tokens, so you can never get them from normal text.

Seeing <tool_call> is a bit misleading because that's just a debug rendering if anything. The front-end sees a special number and knows it's a toolcall. The chat template uses that text form because it's easier than writing the spicy numbers there, but it also has a special parsing mode for those.

The same way it understands what all the other tokens mean -- we throw them at the wall and beat it with a stick until it behaves.

They are specified in the token map as special tokens. Presumably they get trained to use them when they get RL'ed to use tools?