.prompt — Structured Prompts for LLMs
Author .prompt files — a small domain-specific language for writing structured, reusable LLM prompts with variables, conditionals, and branches. The extension compiles them to clean, flat strings ready to send to any model.
Requirements
This extension requires the dot-prompt runtime running locally. The runtime is a Phoenix server distributed as a Docker image.
Start it before using the extension:
docker run -d --name dotprompt -p 4040:4040 dotprompt/runtime-dev:latest
Or with docker-compose if you have the dot_prompt project cloned:
docker-compose up -d
The server runs on http://localhost:4040. The extension connects to it automatically.
Don't have Docker? Get Docker →
Getting Started
- Start the runtime (see above)
- Install this extension from the VS Code marketplace
- Create a file with a
.prompt extension
- Open the Command Palette (
F1) and run .prompt: Compile
That's it. The compiled output appears in a side panel.
The .prompt Language
A .prompt file has two parts: an init block that declares your prompt's metadata and parameters, and a body that uses those parameters to produce text.
A minimal example
init do
@version: 1
def:
mode: assistant
description: A greeting prompt
params:
@name: str = World -> name to greet
@style: enum[formal, casual] = casual -> greeting style
end init
vary @style do
formal: Good day, @name.
casual: Hey @name!
end @style
Compiled with @name: Alice, @style: casual → Hey Alice!
Language Features
Parameters
Declare inputs in the params block. All variables are prefixed with @.
@name: str = World # string with default
@count: int[1..10] = 5 # integer with range
@active: bool = true # boolean
@role: enum[admin, user] = user # enum
Parameters with no default are required at compile time.
Conditionals
if @active is true do
Welcome back!
elif @role is admin do
Admin panel access granted.
else
Please log in.
end @active
Case — deterministic branching
case @language do
en: Hello!
es: Hola!
fr: Bonjour!
end @language
Vary — random branching
Use vary to randomise between options at runtime (requires an enum param):
vary @tone do
formal: I am pleased to assist you.
casual: Happy to help!
end @tone
Fragments
Pull in content from other .prompt files:
{skills}: static from: skills # cached, matched by name
match: @skill_names
{{history}}: dynamic # fetched fresh each request
Lines starting with # are stripped at compile time and never sent to the model.
Commands
| Command |
Description |
.prompt: Compile |
Compile the current file |
.prompt: Open Compiled View |
Open the compiled output panel |
Settings
| Setting |
Default |
Description |
dotPrompt.serverUrl |
http://localhost:4040 |
Runtime server URL |
dotPrompt.autoCompile |
true |
Compile automatically on save |
Troubleshooting
Extension not connecting to the server
- Confirm Docker is running:
docker ps
- Test the runtime directly:
curl http://localhost:4040
- If you're using a different port, update
dotPrompt.serverUrl in settings
Extension not activating
- Make sure your file has a
.prompt extension
- Reload VS Code:
F1 → Developer: Reload Window
Learn More
