Github upload image to pr

Upload Image to PR

Upload local images to a GitHub PR and embed them in the description or comments using browser automation tools.

How It Works

Since the GitHub API does not support direct image uploads, this skill uses the PR comment textarea as a staging area for GitHub's image hosting — uploading files there to obtain persistent user-attachments/assets/ URLs, then updating the PR description or posting a comment via the gh CLI.

Step 0: Resolve PR context

If the user didn't specify a PR number or URL, auto-detect it:

# Get PR number from the current branch
gh pr view --json number,url -q '"\(.number) \(.url)"'

If multiple repos or branches are involved, confirm with the user which PR to target.

Also, normalize the image paths to absolute paths and stage a clean copy inside the current working directory (the repo root) — not /tmp/:

# Stage inside the repo. The staged filename becomes the image's alt text on GitHub,
# so give it a meaningful name. Delete it after the upload completes.
cp /path/to/'CleanShot 2026-... .png' ./.upload-staging.png

Why stage inside the repo and not /tmp/? MCP browser tools (Playwright / Chrome DevTools) can only read files within their configured workspace root, which is normally the project directory the session launched from. A path under /tmp/ is outside that root, so the upload call fails with Access denied: path ... is not within any of the configured workspace roots. Staging the file in the repo works for every backend (agent-browser, a plain CLI, can read /tmp/ too — but in-repo is universally safe).

Staging also sidesteps paths with special characters (e.g. the Unicode narrow spaces CleanShot X puts in filenames), which otherwise break shell globbing and tool arguments. Remember to rm the staged file once you're done so it isn't accidentally committed.

Tool Detection and Selection

Priority Order

1. Chrome DevTools MCP (MCP connection, mcp__chrome-devtools__*) — preferred: connects to existing browser, login state preserved, most stable of the three backends
2. Playwright MCP (MCP connection, mcp__playwright__*) — use only if Chrome DevTools MCP is unavailable; connects to existing browser, login state preserved
3. agent-browser (CLI via Bash — last-resort fallback, login state preserved with --profile)

MCP-based tools connect to an already-running browser instance, so GitHub login state is automatically preserved. agent-browser can persist login state using --profile ~/.agent-browser-github.

Detection

# 1. Search specifically for Chrome DevTools MCP first (preferred, most stable)
ToolSearch: "select:mcp__chrome-devtools__navigate_page,mcp__chrome-devtools__take_snapshot,mcp__chrome-devtools__upload_file,mcp__chrome-devtools__evaluate_script,mcp__chrome-devtools__click"

# 2. Only if Chrome DevTools MCP tools aren't found, search for Playwright MCP
ToolSearch: "browser navigate upload"

# 3. Fall back to agent-browser only if no MCP tools found at all
Bash: agent-browser --version

Tool Compatibility Matrix

Operation	Chrome DevTools MCP (preferred)	Playwright MCP (fallback)	agent-browser (CLI/Bash)
Navigate	navigate_page	browser_navigate	agent-browser --headed open {url}
Snapshot	take_snapshot	browser_snapshot	agent-browser snapshot
Screenshot	take_screenshot	browser_take_screenshot	agent-browser screenshot {path}
Click	click (uid)	browser_click (ref)	agent-browser click {ref}
File Upload	upload_file (uid, filePath)	browser_file_upload (paths)	agent-browser upload {ref} {path}
JS Eval	evaluate_script (function)	browser_evaluate (function)	agent-browser eval '{js}'
Login State	Preserved	Preserved	Preserved with --profile

Steps

Step 1: Navigate to PR page and check login state

Navigate to the PR page and immediately take a snapshot to verify login state.

// Chrome DevTools MCP (preferred)
navigate_page({ url: "https://github.com/{owner}/{repo}/pull/{number}", type: "url" })

// Playwright MCP (fallback if Chrome DevTools MCP is unavailable)
browser_navigate({ url: "https://github.com/{owner}/{repo}/pull/{number}" })

// agent-browser (last-resort fallback; use --profile to persist login state)
agent-browser --headed --profile ~/.agent-browser-github open "https://github.com/{owner}/{repo}/pull/{number}"

If SSO authentication screen appears: Take a snapshot, locate the "Continue" button, and click it.

If NOT logged in (agent-browser only):

1. Navigate to https://github.com/login
2. Ask the user to log in manually in the headed browser window.
3. Wait for user confirmation, then navigate back to the PR page.

Step 2: Locate the upload target

Scroll to the comment form at the bottom of the PR and take a snapshot.

Key gotcha: GitHub's real <input type="file"> (id fc-new_comment_field) is display:none, so it does not appear in the accessibility snapshot — you can't get a uid/ref for it that way, and clicking it isn't possible. Instead, target the visible affordance that opens the file picker: the dropzone labeled "Paste, drop, or click to add files", or the toolbar "Attach files" button. The browser tool clicks it, intercepts the native file chooser, and hands over your file.

In a snapshot these show up as:

button "Attach files"
button "Paste, drop, or click to add files"   ← pass this uid/ref to the upload tool

The comment box itself is a <file-attachment> web component wrapping a <textarea id="new_comment_field"> — that textarea is where the resulting image reference lands (Step 4). GitHub's UI shifts over time, so if new_comment_field isn't there, fall back to textarea[name="comment[body]"] or textarea[id*="comment"]; the PR-description editor instead uses textarea[name="pull_request[body]"] / textarea[id$="-body"].

Step 3: Upload the image(s)

Upload each file with the detected tool, passing the dropzone / attach-button uid from Step 2 (never the hidden input):

// Chrome DevTools MCP (preferred): upload_file({ uid: <dropzone uid>, filePath: <path inside the workspace root> })
// Playwright MCP (fallback):       browser_file_upload({ paths: [<path inside the workspace root>] }) once the file chooser is open
// agent-browser (last resort):     agent-browser upload {ref} {absolute_path}    (any path, /tmp/ ok)

Use the in-repo staged path from Step 0 for the MCP backends (see the workspace-root note there). Wait 2–3 seconds between uploads. For multiple images, upload them all into the same comment box before extracting URLs — more efficient than navigating between uploads.

Step 4: Retrieve the uploaded image URL(s)

While uploading, GitHub shows a placeholder (![Uploading file.png…]()) in the textarea, then swaps it for the final reference once the file lands. So poll the textarea until a user-attachments/assets/ URL appears instead of trusting a fixed sleep — it usually takes 1–5 seconds.

GitHub inserts the reference as an HTML <img> tag (with auto-detected width/height), e.g.:

<img width="342" height="354" alt="filename" src="https://github.com/user-attachments/assets/8fc1b84a-..." />

Don't assume the ![alt](url) markdown form — match the asset URL itself so extraction stays robust to either form:

// MCP-based tools — returns every asset URL plus the raw value for sanity-checking
() => {
  const ta = document.getElementById('new_comment_field')
          || document.querySelector('textarea[name="comment[body]"], textarea[id*="comment"]');
  if (!ta) return { error: 'textarea not found' };
  const urls = [...ta.value.matchAll(/https:\/\/github\.com\/user-attachments\/assets\/[0-9a-fA-F-]+/g)].map(m => m[0]);
  return { raw: ta.value, urls };
}

# agent-browser
agent-browser eval 'const ta=document.getElementById("new_comment_field")||document.querySelector("textarea[id*=comment]");JSON.stringify([...(ta?.value||"").matchAll(/https:\/\/github\.com\/user-attachments\/assets\/[0-9a-fA-F-]+/g)].map(m=>m[0]))'

Keep the whole <img …> tag if you want to preserve GitHub's auto-detected width/height; otherwise take just the URL and wrap it yourself (![alt](url) or your own <img>).

Step 5: Clear the textarea (do not submit the comment)

Dispatch an input event after clearing so GitHub's comment-draft autosave also clears — otherwise the staged content can reappear on the next page load.

// MCP-based tools
() => {
  const ta = document.getElementById('new_comment_field')
           || document.querySelector('textarea[name="comment[body]"], textarea[id*="comment"]');
  if (!ta) return "textarea not found";
  ta.value = "";
  ta.dispatchEvent(new Event('input', { bubbles: true }));
  return "cleared";
}

# agent-browser
agent-browser eval 'const ta=document.getElementById("new_comment_field")||document.querySelector("textarea[id*=comment]"); if(ta){ta.value="";ta.dispatchEvent(new Event("input",{bubbles:true}))} "cleared"'

Step 6: Embed images in the PR

Embed using either the full <img …> tag GitHub gave you (keeps the auto-detected size) or plain markdown ![alt](url).

Option A — Update PR description (append images to existing body):

EXISTING_BODY=$(gh pr view {PR_NUMBER} --json body -q .body)

gh pr edit {PR_NUMBER} --body "$(printf '%s\n\n## Screenshots\n\n%s' "$EXISTING_BODY" '<img width="800" alt="screenshot" src="https://github.com/user-attachments/assets/..." />')"

Option B — Post as a new comment:

gh pr comment {PR_NUMBER} --body '## Screenshots

<img width="800" alt="screenshot" src="https://github.com/user-attachments/assets/..." />'

Use Option A by default unless the user explicitly asks for a comment, or if the PR description is already long and a comment would be cleaner.

Step 7: Verify the result

Reload the page and take a screenshot to confirm the images are displayed correctly.

Tips

• Image sizing: Control display size via HTML <img> tags: <img width="800" alt="description" src="..." />
• Multiple images: Upload all images in one session to the same textarea; extract all URLs before clearing
• Prefer Chrome DevTools MCP: It's the most stable backend — always try it first via ToolSearch. Fall back to Playwright MCP only if Chrome DevTools MCP tools aren't found, and to agent-browser only if no MCP tools are available at all
• agent-browser login persistence: Use --profile ~/.agent-browser-github to persist GitHub login across sessions

Troubleshooting

Issue	Solution
Not logged in (MCP tools)	SSO screen may appear — take snapshot, find "Continue" button, click it
Not logged in (agent-browser)	Use --headed mode, navigate to login page, ask user to log in manually
Browser window not visible	For agent-browser, ensure --headed flag is used
File path with special characters (e.g., Unicode narrow spaces from CleanShot)	Stage a copy with a simple name inside the repo: cp /path/'CleanShot ... .png' ./.upload-staging.png (in-repo so MCP tools can read it — see Step 0)
Access denied: path ... not within any of the configured workspace roots	MCP browser tools only read files inside their workspace root. Stage the image inside the repo (Step 0), not /tmp/
Can't find a uid/ref for the file input	The <input type="file"> is display:none and absent from the snapshot — target the visible "Paste, drop, or click to add files" dropzone or "Attach files" button instead (Step 2)
Textarea has the file but no  markdown	GitHub inserts an <img …> HTML tag for images, not Markdown. Extract the user-attachments/assets/ URL with the regex in Step 4, which matches both forms
Textarea doesn't contain URLs yet	GitHub shows an ![Uploading…]() placeholder first — poll the textarea until a user-attachments/assets/ URL appears (1–5s) instead of a fixed wait
Textarea selector not found	GitHub UI changes occasionally — fall back through new_comment_field → textarea[name="comment[body]"] → textarea[id*="comment"] (Step 2)
Chrome DevTools MCP disconnected	Reconnect via /mcp command
agent-browser not found	npm install -g agent-browser && agent-browser install
No browser tools found	Use ToolSearch to search for available browser tools
PR not found / 404	Private repos return 404 for unauthenticated users — check login state

Notes

• GitHub user-attachments/assets/ URLs are persistent — images remain accessible even without submitting the comment. When rendered, GitHub rewrites them to private-user-images.githubusercontent.com CDN URLs; the user-attachments/assets/... form is the stable one to embed
• On upload, GitHub injects an <img width=… height=… alt=… src=… /> tag (alt is derived from the filename) — not ![](…) markdown. Extract by the asset URL, not the wrapper
• MCP browser tools can only read upload files inside their workspace root, so stage images in the repo, not /tmp/
• Editing the description directly in the browser UI is fragile due to GitHub UI structure changes — updating via gh pr edit is strongly preferred
• Multiple images can be uploaded in a single session before extracting URLs
• MCP-based tools connect to existing browser instances, preserving cookies and login sessions