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 install sudosubin/gh-attach --pin v0.4.2 --force
gh extension list | grep -F 'sudosubin/gh-attach' # require the reviewed v0.4.2 release

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>. Obtain explicit approval before allowing the pinned extension to access that interactive browser profile. Headless and CI uploads are intentionally unsupported: never export, store, or pass a raw user_session cookie to the extension.

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">.
• Keep uploads interactive. Do not place a GitHub browser session in CI, an environment variable, a secret store consumed by this extension, or an agent log.
• 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

• Interactive session cookie required. A user_session cookie grants full account access and is not scoped like a PAT. The supported path is the reviewed, pinned extension reading an explicitly approved local browser profile; CI and headless cookie injection are out of scope.

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