dot-prompt

Language Reference

This reference covers all the syntax elements in the .prompt language.

The One Rule

@ means variable. Always. Only. Everywhere.

Structural keywords never use @.

Init Block

Every .prompt file starts with an init block that declares metadata, parameters, and fragments: 

init do
  @version: 1.0
  @major: 1

  def:
    mode: explanation
    description: Human readable description.

  params:
    @name: type = default -> documentation

  fragments:
    {name}: static from: folder_or_file
    {{name}}: dynamic -> fetched fresh

  docs do
    Free text documentation. Surfaces via MCP.
  end docs

end init

Fields

Field Required Description
@version Yes Semantic version (major.minor)
@major Yes Major version for stability (callers pin to this)
def No Human-readable metadata (mode, description)
params No Input contract
fragments No Fragment declarations
docs No Free-form documentation

Sigils

Sigil Meaning
@name Variable
{name} Static fragment
{{name}} Dynamic fragment
# Comment — never reaches LLM
-> Documentation — surfaces via MCP
= Default value

Operators

Operator Meaning
is Equality
not Inequality
above Greater than
below Less than
min Greater than or equal
max Less than or equal
between Inclusive range

Example

init do
  @version: 1.0
  @major: 1

  params:
    @greeting: enum[hello, hi, hey] = hello
    @name: str

end init

case @greeting do
hello: Hello, @name!
hi: Hi, @name!
hey: Hey, @name!
end @greeting

Next Steps