Context is just one long string. You can do whatever you want with it. Training helps to conform to specific syntactic idiosyncrasies, but LLMs are large enough these days that they can follow pretty much any instructions most of the time.

For example, if you want to use an LLM API that does not natively support tool calls, you can tell the LLM to emit the tool calls for your preferred tools in a markdown code block and parse them yourself.