GitHub Actions "Unable to resolve action" - Fix uses: Reference Errors

A uses: reference points at an action GitHub cannot find: the owner/repo path is wrong, the tag or SHA does not exist, or the action is private and the token has no access.

What this error means

A step fails immediately with "Unable to resolve action <ref>, repository not found" or "unable to find version". No action code runs because the reference cannot be downloaded.

Error: Unable to resolve action actions/checkout@v99, unable to find version v99
# or
Error: Unable to resolve action my-org/private-action@main, repository not found

Common causes

Wrong path or non-existent ref

The owner/repo is misspelled, or the @ref points at a tag, branch, or SHA that does not exist on that action repository.

Private action without access

The default GITHUB_TOKEN cannot read a private action in another repository or org unless access is explicitly granted.

How to fix it

Pin to a real, existing ref

Use the correct owner/repo and a tag or commit SHA that exists. Pinning to a full SHA is the most reliable and secure form.

- uses: actions/checkout@v4
# or pin by commit SHA for supply-chain safety
- uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11

Grant access to a private action

1. Add a token with read access to the action repository, or check out that repo first.
2. In org settings, allow the workflow repository to access the private action repository.
3. Reference local actions with a relative path (./.github/actions/foo) when they live in the same repo.

How to prevent it

• Pin actions to a tag or full commit SHA you have verified exists.
• Use Dependabot to keep action versions current and valid.
• Keep shared internal actions in a repo all consuming repos can read.

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