How to Mention a User in a Slack Webhook: <@ID>, @here and Groups

To mention a user in a Slack webhook, put their member ID inside angle brackets with an @: <@U0123ABCD>. Slack turns it into a real mention and notifies the person. A plain @jane in the webhook text stays plain text. For @here use <!here>, for @channel use <!channel>, and for a user group use <!subteam^S0123ABCD> with the group's ID.

We checked each form on 28 September by sending test messages with Slack's chat.postMessage API to a direct message in our own workspace, then deleting them. Incoming webhooks read the same mrkdwn text.

Slack webhook mention syntax

A full webhook call with a mention looks like this:

curl -X POST -H "Content-Type: application/json" \
  -d '{"text": "<@U0123ABCD> the deploy finished. <!here> please test staging."}' \
  "$SLACK_WEBHOOK_URL"

Slack answers ok with HTTP 200. More payload shapes, and the error codes a webhook returns, are in our Slack webhook curl example.

What we sent and what Slack did

We posted six messages and read them back with conversations.history to see what Slack stored:

• • <@U...> became a mention, stored as a user element.
• • @sieun as plain text stayed plain text.
• • @sieun with "link_names": true became a mention, and Slack stored it as <@U...>.
• • <@U...> inside a Block Kit section with mrkdwn text became a mention.
• • <@U...> inside a Block Kit markdown block became a mention.
• • <@sieun>, a name in the brackets, also became a mention. Slack's docs say to use IDs, and we sent this one with a user token, not a bot or a webhook, so do not rely on it.

This is how the six messages looked in Slack:



link_names is a chat.postMessage argument. We did not test it on an incoming webhook, so for webhooks, send IDs.

How to find a Slack member ID

• Click the person's name or photo in Slack and open their full profile.
• Click More (the three dots).
• Click Copy member ID. It starts with U (or W on Enterprise Grid).

For many people, look IDs up by email with the Web API. users.lookupByEmail needs a bot token with the users:read.email scope. This script finds the ID and posts the mention through a webhook:

import json
import os
import urllib.parse
import urllib.request

BOT_TOKEN = os.environ["SLACK_BOT_TOKEN"]      # xoxb-..., needs users:read.email
WEBHOOK_URL = os.environ["SLACK_WEBHOOK_URL"]  # https://hooks.slack.com/services/...


def user_id_for(email: str) -> str:
    """Look up a Slack member ID from an email address."""
    url = "https://slack.com/api/users.lookupByEmail?" + urllib.parse.urlencode({"email": email})
    req = urllib.request.Request(url, headers={"Authorization": f"Bearer {BOT_TOKEN}"})
    with urllib.request.urlopen(req, timeout=10) as resp:
        data = json.load(resp)
    if not data.get("ok"):
        raise RuntimeError(f"users.lookupByEmail failed: {data.get('error')}")
    return data["user"]["id"]


def post(text: str) -> None:
    body = json.dumps({"text": text}).encode()
    req = urllib.request.Request(WEBHOOK_URL, data=body, headers={"Content-Type": "application/json"})
    with urllib.request.urlopen(req, timeout=10) as resp:
        print(resp.status, resp.read().decode())  # 200 ok


if __name__ == "__main__":
    uid = user_id_for("jane@example.com")
    post(f"<@{uid}> the nightly build failed. Log: <https://ci.example.com/run/42|run 42>")

With a wrong token, users.lookupByEmail returns invalid_auth, and a wrong webhook URL returns HTTP 404 with the body no_team. We checked both of those responses from Slack on 28 September. Store the ID once you have it; member IDs do not change when someone renames themselves.

Mention @here, @channel and user groups from a webhook

• @here notifies active members of the channel: <!here>.

• @channel notifies every member of the channel: <!channel>. Use it rarely; see @here vs @everyone vs @channel.

• A user group, such as @oncall, needs the group's ID: <!subteam^S0123ABCD>. Find it with usergroups.list. Setting up groups is in Slack user groups.

Slack's formatting docs add one rule: a user mentioned by an app is notified only if they are already in the channel. If a mention shows as a name but nobody gets a notification, check that the person is a member of the webhook's channel.

Slack webhook mention not working

• You sent @name. Replace it with <@MemberID>.

• The text is plain_text or has "mrkdwn": false. Mentions only parse in mrkdwn text.

• The brackets were escaped. If your code replaces < with < in the whole message, it breaks the mention too. Escape only the user text you insert, not your own <@...> tokens.

• The person is not in the channel. The mention shows, but Slack does not notify them.

• You used the display name as an ID. IDs look like U0123ABCD, not jane.doe.

To check a message before you send it, paste the text into the Slack message formatter. If your source text is standard markdown, run it through the markdown to Slack converter first; in mrkdwn, **bold** and [text](url) stay literal, so the converter rewrites them as *bold* and <url|text>.

Mentions in Block Kit, Workflow Builder, n8n and GitHub Actions

• Block Kit. Put <@U0123ABCD> in a mrkdwn text object, or in a markdown block. Both worked in our test. The rest of the syntax is in Slack Block Kit markdown.

• Workflow Builder. In a "Send a message" step, insert the variable for the person, such as "Person who used this workflow". Examples are in Slack Workflow Builder examples.

• n8n, Zapier and other HTTP tools. Build the same text with the ID: <@{{ $json.slackId }}> in n8n. The tool only sends the string; Slack does the parsing.

• GitHub Actions. Map GitHub usernames to Slack IDs in a secret or a file, then send <@ID>. The workflow is in how to send a Slack message from GitHub Actions.

FAQ

How do I tag someone in a Slack webhook message?

Use their member ID in angle brackets: <@U0123ABCD>. Copy the ID from their profile under More, Copy member ID.

How do I send @here with a Slack webhook?

Put <!here> in the text. <!channel> sends @channel.

Can a Slack webhook mention a user by name?

Not reliably. Plain @name stays text. Look up the ID by email with users.lookupByEmail and send <@ID>.

How do I mention a user group in a Slack webhook?

<!subteam^S0123ABCD>, with the group's ID from usergroups.list.