Gh Attach

Upload and download GitHub user-attachments (gh-attach)

GitHub has no public API for user-attachments. The web UI uses an internal endpoint that mints github.com/user-attachments URLs whose visibility follows the repository they belong to. gh-attach (MIT, sudosubin) replicates that drag-and-drop flow as a gh CLI extension, so an agent can upload a local file from the terminal, get a URL back, and later download an attachment URL to a file.

Overview

This skill drives gh-attach to turn a local file (screenshot, image, PDF, zip, log, or video) into a hosted GitHub user-attachments URL, then embeds that URL into a pull request, issue, or comment. It also downloads an existing attachment URL back to a local file. GitHub auto-renders the URL as an image, video, or file wherever it is pasted, and the URL inherits the repository's visibility, so a private-repo upload stays private. It works against GitHub Cloud and GitHub Enterprise Server.

When to Use This Skill

Use this skill when asked to:

• "Attach a screenshot to the PR" or "add an image to the PR description"
• "Attach this file (PDF, zip, log, video) to the issue or comment"
• "Embed before/after screenshots" in a PR, issue, or README
• "Download this GitHub attachment" from a user-attachments URL

How It Works

Step 1: Verify prerequisites

gh auth status                                   # gh installed and authenticated
gh extension list | grep -q 'gh attach' \
  || gh extension install sudosubin/gh-attach    # review/pin the extension source first

Uploads use a GitHub user_session browser cookie, not the gh token (that endpoint rejects tokens). By default gh must be authenticated so gh-attach can select the matching browser account (Chromium family, Firefox family, or Safari). If the wrong account is selected, add --browser <name> --profile <name>. For headless or CI use, set GH_ATTACH_SESSION_TOKEN to the bare user_session cookie value and treat it as a full account credential.

Step 2: Upload

# Use an absolute quoted path; -R is optional inside a repo working dir.
URL=$(gh attach "/abs/path/screenshot.png" -R <owner>/<repo>)

gh attach prints the URL on one line to stdout. For GitHub Enterprise Server, use -R host/owner/repo. Capture the output; it is the embeddable reference.

Step 3: Embed into the PR / issue / comment

printf '## Screenshots\n\n%s\n' "$URL" \
  | gh pr comment <pr> -R <owner>/<repo> --body-file -

Use gh pr edit, gh issue comment, or gh issue edit with --body-file - for other targets. Always pass --body-file - (not inline --body) so multi-line bodies and special characters cannot break shell quoting. GitHub auto-renders the URL, so paste it as-is.

Step 4: Download

# Specify the destination explicitly.
gh attach download "$URL" -O "/abs/path/out.png"

Downloads of private attachments use the active gh token, with browser cookies as an authorization fallback.

Examples

• Attach a screenshot to PR #42: upload the file, then append the URL under a ## Screenshots heading in the PR body with gh pr edit ... --body-file -.
• Embed before/after screenshots in a README: upload both files, paste the two URLs into the README at the relevant section.
• Download an attachment for review: run gh attach download "$URL" -O out.zip to fetch a user-attachments file locally.

Best Practices

• Resolve globs to absolute paths first, and quote paths that contain spaces or Unicode.
• For display sizing, embed an HTML tag instead of the bare URL: <img width="800" src="$URL">.
• In CI, set GH_ATTACH_SESSION_TOKEN from a dedicated bot account.
• gh-attach can upload multiple files concurrently and emit Markdown or JSON output with jq-style filtering when you need to script around the result.

Limitations

• Session cookie required. A user_session cookie grants full account access (it is not scoped like a PAT), so treat it like a password and prefer a bot account in CI.
• Write access to the target repo is required to upload.
• Private-repo attachments stay private: the user-attachments URL inherits repo visibility, so an anonymous fetch on a private repo returns 404 or 403 by design.
• GitHub Cloud and GitHub Enterprise Server each decide which file extensions and content types they accept.
• The skill embeds the URL itself; gh attach only prints it.

Security & Safety Notes

• The user_session cookie and GH_ATTACH_SESSION_TOKEN are full-account credentials. Never print them, never paste them on a command line, and never commit them. Prefer a dedicated bot account for headless or CI use.
• Uploaded attachments are auto-rendered by GitHub, so only upload files you intend to share with everyone who can view the target repository.
• Confirm the destination -R <owner>/<repo> before uploading so an attachment is not created against the wrong repository.