Template Variable Substitution With Default Value Syntax

| [Hugging Face Dataset](https://huggingface.co/datasets/fka/prompts.chat) |

Unique: Uses a simple `${VariableName:DefaultValue}` syntax for inline variable substitution within markdown prompts, allowing templates to be self-contained with fallback defaults. This approach prioritizes human readability over formal specification, making templates easy to read and edit in any text editor without special tooling.

vs others: More readable and portable than Jinja2 or Handlebars templating because it uses a minimal, domain-specific syntax that doesn't require learning a full template language, but less robust because it lacks validation and error handling.