Surface is a small KDL format for describing an application without prescribing its implementation. It gives humans and LLMs a shared, checked product specification: data, capabilities, interfaces, screens, technology choices, context, and ordered logic.
It adds just enough syntax to describe an application with the ability to add LLM context to kdl nodes.
Status: experimental · Format: Surface 0.1 · Syntax: KDL 2 · Extension:
.kdl
/- kdl-version 2
surface "0.1"
application "todo" {
purpose "Keep a small list of tasks."
stack "web" {
target "browser"
technology "markup" "html"
technology "styling" "css"
}
}
collection "todo" {
(string)"text"
(boolean)"completed"
}
(array)value "todos" variable {
context (collection)"todo" "Contain the current todos."
}
function "createTodo" {
collection "todoInput" {
(string)"text"
}
input (collection)"todoInput"
output (collection)"todo"
logic {
(collection)"todoInput" "Trim the text and output null if it is empty."
(collection)"todo" "Otherwise, output a todo with that text and completed set to false."
}
}
interface "todoList" {
context (value)"todos" (function)"createTodo" "Render a text input, an Add button, and the current todos."
logic {
(value)"todos" "Start with this value empty."
(function)"createTodo" "When Add is activated, call this function and append its output when it is not null."
(collection)"todo" "Let the user toggle each todo between complete and incomplete."
}
}
screen "home" {
use (interface)"todoList"
}
Surface currently builds locally from source. Install mise, then build and install the CLI for your user:
git clone https://github.com/etoxin/surface.git
cd surface
mise install
mise run build
install -d "$HOME/.local/bin"
install -m 755 build/surf "$HOME/.local/bin/surf"
Make sure your ~/.zshrc
contains:
export PATH="$HOME/.local/bin:$PATH"
Open a new terminal and confirm the installation:
surf --help
This installation path currently supports macOS only.
Enter a directory containing a surface.kdl
file, then run:
surf init
Select Codex, Claude Code, or both. The command installs their project-local Surface
skills and adds /build/
to .gitignore
. Use surf init --codex
, surf init --claude
, or both flags for a non-interactive setup.
To have an LLM create the specification as well as the application, follow Create a Specification with an LLM.
Start with Getting started to write and implement your own
specification. Surface is experimental, so keep the .kdl
source in version control and review generated applications before using them.
| Guide | Purpose |
|---|---|
Getting startedGenerating applicationsTesting and reportingSurface 0.1 grammarStarting a Surface fileApplicationTechnology stacksPortable typesValues and enumsCollectionsFunctionsInterfacesScreensContextLogicFive examples cover the workflow from first use through platform-scale tests:
Hello WorldCreate a Specification with an LLMTodo ListOnline CheckoutMulti-tenant Project Tracker
Online Checkout and Multi-tenant Project Tracker pin Pico CSS 2.1.1 in their application stacks and test the frozen grammar at platform scale.
Each example is its own agent workspace. Enter one and initialize it with the installed CLI:
cd examples/todo-list
surf init
Select Codex, Claude Code, or both, then open that agent in the example directory. Run
$surf-build
in Codex or /surf:build
in Claude Code. Both build surface.kdl
into
build/
; generated build directories are ignored by Git.
surf init [--codex] [--claude]
surf parse <file.kdl>
surf check <file.kdl>
surf format <file.kdl>
surf reference <file.kdl> <selector|--list>
reference --list
discovers selectors and typed reference literals. Passing a selector prints its complete KDL declaration for focused human or LLM context.
For repository development, run mise tasks
to see the available tasks. The complete
repository check is mise run verify
.
Surface 0.1 is frozen. Bug fixes, diagnostics, formatting, documentation, and tooling may improve, but new valid syntax belongs to a later format version.