---
id: codemods
title: Codemods
slug: /guides/codemods/
description: Relay guide to codemods
keywords:
  - codemod
  - codemods
---

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The Relay compiler has the ability to make changes across the source files of
your projects with the use of codemods. You can see the list of codemods
available by running the Relay compiler's `codemod` command:

```
> relay codemod --help
Apply codemod (verification with auto-applied fixes)

Usage: relay codemod [OPTIONS] [CONFIG] <COMMAND>

Commands:
  mark-dangerous-conditional-fragment-spreads  Marks unaliased conditional fragment spreads as @dangerously_unaliased_fixme
  remove-unnecessary-required-directives       Removes @required directives from non-null fields within @throwOnFieldError fragments and operations.
  fix-all                                      Runs all Relay compiler transforms and fixes all fixable diagnostics
  help                                         Print this message or the help of the given subcommand(s)

Arguments:
  [CONFIG]  Compile using this config file. If not provided, searches for a config in package.json under the `relay` key or `relay.config.json` files among other up from the current working directory

Options:
  -p, --project <project>  Compile only this project. You can pass this argument multiple times. to compile multiple projects. If excluded, all projects will be compiled
  -h, --help               Print help
```

## Available codemods

The compiler currently has these available codemods:

### mark-dangerous-conditional-fragment-spreads

This codemod finds fragment spreads that are _dangerously unaliased_; that is,
the fragment might not be fetched due to a directive such as `@skip` or its
inclusion on a mismatched type within a union. If such a conditional fragment is
not aliased with [`@alias`](../alias-directive/), there is no way for the
resulting generated Flow or TypeScript types to reflect its nullability. This
codemod will add the `@dangerously_unaliased_fixme` directive to such fragment
spreads, indicating to developers that there is a problem to be fixed. After
applying this codemod, the `enforce_fragment_alias_where_ambiguous` feature flag
can be enabled, which will ensure any future ambiguous fragment spreads must be
aliased.

Since this codemod can potentially modify many files, there is an optional
`--rollout-percentage` parameter (shorthand: `-r`) which, if used alongside the
`enforce_fragment_alias_where_ambiguous` feature flag in rollout mode, allows
progressive codemod and enforcement of this validation.

### remove-unnecessary-required-directives

Removes [@required](../api-reference/graphql/graphql-directives.mdx#required)
directives from non-null fields within
[@throwOnFieldError](../api-reference/graphql/graphql-directives.mdx#throwonfielderror)
fragments and operations, or linked fields with
[`@catch`](../guides/catch-directive.mdx), where the compiler is certain that the
directive does not change the generated types for the data being fetched.

### fix-all

Runs all Relay compiler transforms and automatically applies fixes for every
fixable diagnostic. This is a convenient catch-all codemod to apply when
upgrading Relay versions — run it after updating the package to repair any
issues the compiler now flags:

```sh
relay codemod fix-all
```