Your first program

Making a project takes one command, and it has one choice in it: which AI assistant you use. If you run weft new hello with no flag, weft asks you, listing the assistants it found on your machine first. Or pass --assistant with your row from this table. Either way weft copies Tangle into the project. Tangle is a persona that teaches your assistant the language, and it reads the catalog on your disk rather than trusting what it remembers.

If weft is run from a script or by an AI agent, there is nobody to ask, so it stops and lists these values: pass one. If you use more than one assistant, pass --assistant once for each. When weft asks, it also asks whether to keep your answer for later projects. A flag is for this project only, so if you want your next weft new to install the same one with no flag, add --remember, as here:

weft new hello --assistant claude-code --remember
cd hello
weft run

weft run says it is building, then prints the project’s name and id, then the run’s id and how many nodes it runs, then a line for every node as it starts and finishes, then a tick:

building hello
registered hello (3f2a1c4e-9b81-4d0a-8e55-7c2f1a6b30de)
started run 9b81d0a2-4e17-4a33-bc90-51d8e2f4a7c1 on version a1b2c3d4
2 nodes
→ started run=9b81d0a2 entry=greeting
  …
✓ completed run=9b81d0a2

hello uses only the standard library’s nodes, so on your machine it runs the worker program weft ships ready-made (the standard worker), and nothing compiles. Once a project has nodes of its own, or infrastructure, its build prints two lines for each worker it compiles and each infrastructure image it builds, indented under the rest:

  building <image> as <build>; its log: <url>
  built <image> in about <time>

The ; its log: <url> part shows only when the build has a log to point at.

That long id after started run is the run’s id, and it is how you point at this one run later. Everything that reads a run takes it, and the first eight characters are enough as long as they name only one.

If weft is not found, open a new terminal; the installer’s PATH line only takes effect in a fresh one. If the run stops saying it cannot reach the runtime, run weft daemon status and go back to Install.

See it as a graph

Open the hello folder in VS Code, click the Weft icon in the bar down the left edge, and click your project under Projects. The source opens on the left and the graph opens beside it. (If you opened src/main.weft yourself, click Open Graph to the Side in the file’s title bar.)

Type in either pane and the other updates.

This is what weft new wrote, and what you just ran:

greeting = Text { value: "Hello, World!" }
out = Debug { data: greeting.value }

Two boxes and an arrow. A box is a node. The dots down its left edge are what it takes in, the dots down its right edge are what it sends out, and each dot is coloured by the kind of value it carries, so two dots of the same colour fit together.

The arrow is greeting.value sitting where out’s data input goes. Writing a source and a port where a value belongs is how you connect two nodes, and it is the only wiring syntax there is.

While a run is going, each box glows: amber while it works, cyan while it waits for something, grey while it is paused only because its run paused, green when it finished, red when it failed. Click the magnifying glass on a box to see exactly what went in and what came out.

For adding a box and drawing an arrow yourself, go and read working in the graph.

What weft new made

Two more folders turn up later rather than now: layouts/, the first time you drag a box, and assets/, when something needs a prompt or a script kept in a file of its own.

weft new also runs git init and writes a .gitignore. Tangle’s files are ordinary project files, so they commit with the rest and anyone who clones your project gets Tangle without installing weft.

Next, the three lifecycles: what starts on its own and what does not.