Linter

The linter checks YAML files the way tinyaml loads them. It reports YAML tinyaml can't load, with the line and column, and plain values that load as strings here but that other YAML readers take for a boolean, null, a number, or a date.

It runs from the command line, as a library, as an ESLint plugin, or as a Vite Doctor extension. It all ships with tinyaml. The command line and the library need nothing else, and the ESLint plugin and the Vite Doctor extension need ESLint or Vite Doctor installed.

pnpm add -D tinyaml
pnpm tinyaml-lint "**/*.{yaml,yml}"

It prints one line per problem and exits with 1 if there are any:

config.yaml:1:8 tinyaml/ambiguous-value `no` loads as the string "no", but YAML 1.1 readers such as PyYAML read it as a boolean. Quote it to keep the string, or write `true` or `false`.
site.yaml:3:13 tinyaml/invalid-yaml tinyaml can't load this YAML: duplicated mapping key. Fix the YAML at this position.

Globs skip node_modules and dist. --format json prints the problems as a JSON array instead.

import { lint } from "tinyaml/linter";

lint("draft: no\n");
// [{ rule: "tinyaml/ambiguous-value", severity: "warn", line: 1, column: 8, message: "…", fix: "…" }]

lint takes one YAML stream and never throws. lintFiles(files, read) lints several files, reading each one with read. rules maps each rule to its Vite Doctor code, title, and severity.

tinyaml throws on this YAML, so parse and parseAll fail. The linter reports tinyaml's message at the line and column it names.

# ❌ the second `title` throws `duplicated mapping key`
title: Hello
title: World

# ✅
title: Hello

tinyaml reads YAML with the YAML 1.2 core schema. Other readers turn more plain values into something else: js-yaml's default schema reads 0b10, 1_000, and 2026-11-01 as numbers and dates, and YAML 1.1 readers such as PyYAML read yes, no, on, and off as booleans. The same file gives different data depending on who reads it. Values tinyaml already parses as booleans, null, or numbers, such as True, ~, 0x10, and .inf, are not reported.

# ❌ a string here, a boolean in PyYAML
draft: no

# ✅ the same in every reader
draft: false
title: "no"

Quote the value to keep the string, or write the JSON value you meant. Quoted values, block scalars, and comments are never reported.