file_header

The first N lines must match a regex (line-oriented). For a byte-level prefix check, prefer file_starts_with.

- id: spdx-header
  kind: header
  paths: "src/**/*.rs"
  pattern: "^// SPDX-License-Identifier: MIT"
  level: error

Fix: file_prepend — inject declared content at the top (preserves UTF-8 BOM).

Options

Option	Type	Required	Default	Description
lines	integer (>= 1)		20	Number of leading lines to consider.
pattern	string	yes		Rust regex. The first lines lines of each file in scope must match.

Plus the common paths, level, id, and when fields. This table is generated from the JSON Schema; option types and defaults are authoritative.