01. FACET v2.1.3 Quick Start

This quick start uses only normative FACET v2.1.3 syntax.

1) Install

cargo install --git https://github.com/rokoss21/facet-compiler --bin facet-fct
facet-fct --version

Optional alias:

alias fct=facet-fct

2) Create a minimal file

Create hello.facet:

@meta
  version: "1.0"
  author: "Quick Start"

@context
  budget: 32000

@vars
  name: "World"
  greeting: "Hello"

@system
  content: "You are a helpful assistant."

@user
  content: "$greeting, $name!"

3) Validate and run

facet-fct build --input hello.facet
facet-fct run --input hello.facet --format pretty

Expected canonical JSON shape:

{
  "metadata": {
    "facet_version": "2.1.3",
    "profile": "hypervisor",
    "mode": "exec",
    "host_profile_id": "...",
    "document_hash": "sha256:...",
    "policy_hash": null,
    "policy_version": "1",
    "budget_units": 32000,
    "target_provider_id": "..."
  },
  "tools": [],
  "messages": [
    { "role": "system", "content": "You are a helpful assistant." },
    { "role": "user", "content": "Hello, World!" }
  ]
}

4) Add pipeline transforms

@vars
  raw_query: "  What is FACET?  "
  query: $raw_query |> trim() |> lowercase()

@system
  content: "Answer briefly and clearly."

@user
  content: $query

|> is the FACET pipeline operator. In v2.1.3, standard Level-0 lenses are listed in Appendix A.

5) Add runtime input (@input)

@vars
  query: @input(type="string") |> trim()

@system
  content: "You are a helpful assistant."

@user
  content: $query

Create runtime.json:

{ "query": "  Explain R-DAG in FACET  " }

Run:

facet-fct run --input input.facet --runtime-input runtime.json --format pretty

6) Common invalid patterns (spec violations)

The following are not valid FACET v2.1.3 message fields and should fail with F452:

@system
  role: "assistant"
  model: "vendor-model"
  instructions: "..."

@context is for layout budget/defaults, not RAG documents. This is invalid:

@context
  documents: ["..."]

7) Next pages

1. Tutorial
2. Examples Guide
3. CLI Reference
4. Error Codes