gh-attach – Coding skill for AI agents

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](https://github.com/sudosubin/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 42 -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.

• 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 is a full-account credential. Never print, export,

paste, log, or commit it, and never make it available to CI or headless agents.

• Do not install or upgrade gh-attach from a moving branch or an unpinned latest

release. Re-review and update the exact --pin only in a repository change.

• 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.