Improve error message when branch doesn't exist (e.g., suggest trying `master`)

[ivan-magda]

Description

When fetching a repository fails due to an incorrect branch name, the error message "GitHub API Error:" provides no actionable guidance to the user.

Steps to Reproduce

1. Go to https://githubtree.mgks.dev
2. Enter matteocrippa/awesome-swift
3. Leave branch as main (default)
4. Click "Fetch"
5. See unhelpful error: "GitHub API Error:"

Current Behavior

• Generic "GitHub API Error:" message with no details
• User has no idea what went wrong or how to fix it

Suggested Improvement

When a 422 error occurs on the commits endpoint, display a more helpful message like:

Branch not found. The branch main doesn't exist in this repository. Try master or check the repository for available branches.

Or even better — auto-detect the default branch using the Repos API which returns a default_branch field.

Environment

• Browser: Chrome
• Date: Jan 4, 2026

[mgks]

Thanks again for this suggestion.
You are absolutely right, showing a generic 404/422 error was a poor experience.

I have implemented auto-detecting the default branch.

• Smart Fallback: If you request a branch (e.g., main) and it fails, the tool now checks the repository metadata, finds the actual default branch (e.g., master), and fetches that instead.
• Clear Feedback: The UI (and CLI) will explicitly tell you: "Branch main not found. Switched to master."
• Better Errors: If the repo itself is missing or private, we now show a specific error message instead of a generic API error.

The fix is live now, give it a go - GitHubTree, and package has also been updated npm install gh-tree@latest.

Let me know if this solves it for you! ✌🏼

[ivan-magda]

Let me know if this solves it for you! ✌️

Thanks, it works 👍