Linkedin Reply API

LinkedIn Reply API (Voyager)

Post comments on LinkedIn posts programmatically via LinkedIn's internal Voyager API. No browser clicking or navigation to individual posts needed — just run JavaScript on any linkedin.com page.

Prerequisites

• Chrome browser with LinkedIn open and logged in
• Chrome MCP extension connected (mcp__claude-in-chrome__* tools available)
• Must be on any linkedin.com page (needs session cookies)

Verify Chrome MCP is available:

mcp__claude-in-chrome__tabs_context_mcp

If it errors: tell the user "Chrome MCP isn't connected. Open Chrome with the Claude extension active."

How It Works

1. Extract the activity ID from the post URL
2. Extract the CSRF token from session cookies
3. POST to the Voyager comment endpoint
4. Get 201 Created on success

Extracting the Activity ID

The activity ID is the only identifier you need. Use it directly as urn:li:activity:{ID} for posting. No resolution step needed — this works for all post types (ugcPost-backed and share-backed).

From Post URL

// URL: https://www.linkedin.com/posts/someone_some-text-activity-7424806492844949504-xxxx
// or:  https://www.linkedin.com/feed/update/urn:li:activity:7424806492844949504
const activityId = postUrl.match(/activity[:-](\d+)/)?.[1];

From Apify/Scraper Output

// post.id = "urn:li:activity:7424806492844949504"
const activityId = post.id.split(':').pop(); // "7424806492844949504"

Posting: One Comment Per Tool Call

Do NOT batch multiple comments in one javascript_tool call. The Chrome MCP extension times out after ~10 seconds. Scripts with await delays get "Detached" errors, but the fetches keep running silently in the browser, causing duplicate posts if you retry.

Post one comment at a time, with separate tool calls for each:

(async () => {
  const activityId = 'ACTIVITY_ID';     // numeric ID extracted above
  const commentText = 'COMMENT_TEXT';

  const csrf = document.cookie.match(/JSESSIONID="([^"]+)"/)?.[1];
  if (!csrf) return JSON.stringify({ error: 'No JSESSIONID' });

  const response = await fetch(
    '/voyager/api/voyagerSocialDashNormComments?decorationId=com.linkedin.voyager.dash.deco.social.NormComment-43',
    {
      method: 'POST',
      headers: {
        'accept': 'application/vnd.linkedin.normalized+json+2.1',
        'content-type': 'application/json; charset=UTF-8',
        'csrf-token': csrf,
        'x-restli-protocol-version': '2.0.0'
      },
      body: JSON.stringify({
        commentary: {
          text: commentText,
          attributesV2: [],
          '$type': 'com.linkedin.voyager.dash.common.text.TextViewModel'
        },
        threadUrn: 'urn:li:activity:' + activityId
      })
    }
  );

  const status = response.status;
  if (status === 201) {
    return JSON.stringify({ success: true, status, commentUrn: response.headers.get('x-restli-id') });
  } else {
    let error;
    try { error = await response.json(); } catch { error = await response.text(); }
    return JSON.stringify({ success: false, status, error });
  }
})()

Wait 3-5 seconds between each tool call (the delay lives between calls, not inside the script).

API Reference

Comment Endpoint

POST /voyager/api/voyagerSocialDashNormComments
  ?decorationId=com.linkedin.voyager.dash.deco.social.NormComment-43

Request Headers

Request Body

{
  "commentary": {
    "text": "Your comment text here",
    "attributesV2": [],
    "$type": "com.linkedin.voyager.dash.common.text.TextViewModel"
  },
  "threadUrn": "urn:li:activity:7424806492844949504"
}

Response

Success: 201 Created

• x-restli-id header contains the comment URN
• Body: { "data": {...}, "included": [...] }

Response Codes

Browser Fallback

If the Voyager API returns 403 (session expired) and refreshing doesn't help, use the browser DOM method. See references/browser-fallback.md.

Troubleshooting

Historical Note

Earlier LinkedIn API docs said the comment API required urn:li:ugcPost:XXX and that activity URNs needed resolution via GET /voyager/api/feed/updates/. Testing confirmed urn:li:activity:{ID} works directly as threadUrn for all post types (both ugcPost-backed and share-backed). The resolution step is unnecessary.

Reverse-engineered Feb 2026. LinkedIn can change internal APIs at any time. If calls start failing, re-intercept via DevTools Network tab.