# Type checking

`avril check` type-checks an entry module and its whole Avril module graph
without executing any of it:

```sh
avril check --typescript=/absolute/path/to/package/lib/tsc main.ts
```

`--typescript=PATH` names the same pinned, unmodified native TypeScript
backend as `avril lsp`; see the [download instructions](../lib/lsp/BACKEND.md).
`--typescript PATH` is also accepted.

Checking shares the language server's resolution and compiler settings
rather than a generated `tsconfig.json`: `avril.conf` import maps and package
ownership, `jsr:`/`npm:`/`https:` dependencies, `avril:` builtin declarations,
per-file JSX settings, and the cache/lock/vendor policy selected by the usual
package flags (`--offline`, `--frozen`, `--lock=PATH`, `--vendor=PATH`, …).
The `types.imports` map can redirect module resolution for types only, and
`types.globals` explicitly lists global declaration modules; neither changes
runtime imports, nor are npm packages automatically added as globals merely
because they are present. npm `@types` discovery is recorded during `add`,
`cache`, `update`, and `vendor` (including negative results), then replayed from
the lock by check and the language server. Use `avril cache main.ts` to prepare
it first, or `--no-types-packages` to disable automatic DefinitelyTyped lookup
without disabling bundled or explicitly configured declarations.
See [npm type declarations](npm.md#type-declarations).
Capability flags (`-0`, `--allow-*`, `--deny-*`) apply as they do for
`avril cache`. As with the language server, checking may populate the package
cache but never writes lockfiles, tsconfigs, or application sources.

Diagnostics are printed one per line as
`path:line:column: error TS2322: message`, using the original source
locations. The command exits nonzero if any error is reported; warnings are
printed but do not fail the check. A clean graph prints nothing.