Write a lang package

A lang package teaches an agent how to write in a language or a notation: the idioms, the constraints, the shape of a good file. This page writes one and explains how vibe recognises it as a language discipline.

Create a lang package org.acme/sql-style in the current VibeVM project, as an in-tree package under vibevm/vibepacks/: a guide on how our team writes SQL. Give it a boot snippet that names the three rules an agent must always follow, and a guide document with the full idioms, examples and the reasons behind them. Run vibe check on it. the vibevm skill installed for your agent; a project with `vibe.toml` at the root `vibevm/vibepacks/org.acme/sql-style/v0.1.0/vibe.toml` declares `kind = "lang"` with a boot snippet; the guide under `vibevm/vibespecs/` has anchored sections the snippet cites; `vibe check` reports no errors vibe check --path vibevm/vibepacks/org.acme/sql-style/v0.1.0 --quiet grep -q "kind = \"lang\"" vibevm/vibepacks/org.acme/sql-style/v0.1.0/vibe.toml

The agent creates the package skeleton, writes the guide and its snippet the way a flow's are written, and sets the kind to `lang`. The difference from a flow is the genre, not the mechanics. A flow says how the team works; a lang package says how to write in something. The kind tells an agent, a [registry](../glossary/index.xml#registry) and the site which is which before the file is opened.

The genre is wider than programming languages: a guide to a query language, a configuration notation, a documentation dialect or a house style of a language all fit. What does not fit is a bundle of tools; that is a stack. The examples in the public registry are the AI-Native language guides for Rust, TypeScript and Go, each shipping a guide, a set of cards and a runnable toolchain.

An AI-Native language is recognised by one thing only: its dependency on the shared discipline core, `org.vibevm.ai-native/core-ai-native`. Not by its group, not by its name. A third party may publish its own language discipline in its own group and be recognised the same way, so the discipline is not a closed club.

A language guide that also ships tools, a checker, a formatter, a type oracle, becomes a [family](../glossary/index.xml#family). The guide package is `<family>-lang`; a server package `<family>-mcp` serves the same tools to agents; a bundle `<family>` pins both at one version. The members move in unison; a consumer requires the bundle and gets a tested set.

The family stem leads every named surface: crates, binaries, [skills](../glossary/index.xml#skill) and the server all carry the `<family>` prefix, so everything of one language sorts and reads together.

1. Create the package slot, then set `kind = "lang"` in its [manifest](../glossary/index.xml#manifest):

vibe init package org.acme/sql-style Creating package `org.acme/sql-style` in `<TMP>/work` ✓ created vibevm/vibepacks/org.acme/sql-style/v0.1.0/vibe.toml ✓ created vibevm/vibepacks/org.acme/sql-style/v0.1.0/vibevm/vibespecs/boot/10-tool-sql-style.md ✓ created vibevm/vibepacks/org.acme/sql-style/v0.1.0/README.md • kept vibevm/vibespecs/boot/INDEX.md (regenerated) • kept CLAUDE.md (regenerated) • kept AGENTS.md (regenerated) • kept GEMINI.md (regenerated) Done. Project `org.acme/sql-style`: 3 files created, 4 kept. Next: • edit vibevm/vibespecs/boot/00-core.md and vibevm/vibespecs/common as your project takes shape • install packages with `vibe install <kind>:<name>` (e.g. flow:wal)

2. Inside the slot, write `vibevm/vibespecs/boot/sql-style.xml` with the rules an agent must follow every time. Put the guide under `vibevm/vibespecs/lang/sql-style/`, with the reasons, the idioms and the examples.

3. Declare `[boot_snippet] source = "vibevm/vibespecs/boot/sql-style.xml"`, `category = "stack"`, so that the language rules come after the team's flows in a consumer's reading list.

4. Check: `vibe check --path vibevm/vibepacks/org.acme/sql-style/v0.1.0`.

What a language brought that can be run is answered by `vibe tools`, not by the kind: the [boot lane](../glossary/index.xml#boot-lane) says which disciplines are installed, the tools registry says what they brought.

Before the `lang` kind existed, language guides were stacks; a `stack` package that is really a guide should move to `lang` at its next version, so that the word means one thing.