slackapi/slack-github-action v4: Send a Slack Message From GitHub Actions

slackapi/slack-github-action is Slack's official GitHub Action for posting to Slack from a workflow. The latest release is v4.0.0 (15 July 2026, commit dcb1066). Add it as a step, give it either a bot token with method: chat.postMessage or an incoming webhook URL, both stored as repository secrets, and write the message in the payload input as YAML. Add if: failure() to post only when a build breaks, and errors: true so a Slack error fails the step: on 6 October we ran v4.0.0 against a wrong channel ID and, with the default errors: false, the step still exited 0.

How bot tokens differ from user tokens is in Slack bot token.

Four ways to post to Slack from GitHub Actions

The action is maintained by Slack. To pin it to an exact build, as many security policies require, use the commit instead of the tag: uses: slackapi/slack-github-action@dcb1066f776dd043e64d0e8ba94ca15cc7e1875d # v4.0.0. Version 4.0.0 came out on 15 July 2026; its one breaking change is stricter YAML in payload, where a value that spans several lines must be indented under its key. Version 3 moved the action to the Node.js 24 runtime, so old self-hosted runners may need an update.

Option 1: bot token and chat.postMessage

This way can post to any channel the bot is in, reply in threads and edit its own messages.

• Create a Slack app at api.slack.com/apps, or use an existing one.
• Under OAuth & Permissions, add the bot scope chat:write.
• Click Install to Workspace and copy the Bot User OAuth Token (it starts with xoxb-).
• In GitHub, open Settings > Secrets and variables > Actions and add SLACK_BOT_TOKEN. Add the channel ID as SLACK_CHANNEL_ID; you find it at the bottom of the channel's details panel.
• In Slack, run /invite @your-app in that channel. Without it, the call fails with not_in_channel.

Then add the step. This workflow runs tests on every push to main and posts only if they fail:

name: CI
on:
  push:
    branches: [main]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - run: npm ci && npm test

      - name: Tell Slack the build failed
        if: failure()
        uses: slackapi/slack-github-action@v4.0.0
        with:
          method: chat.postMessage
          token: ${{ secrets.SLACK_BOT_TOKEN }}
          errors: true
          payload: |
            channel: ${{ secrets.SLACK_CHANNEL_ID }}
            text: ":x: ${{ github.workflow }} failed on ${{ github.ref_name }}: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"

We parsed this file and its payload block with a YAML parser to check the indentation that v4 requires.

What happened when we ran v4.0.0 against Slack

On 6 October 2026 we checked out the v4.0.0 tag and ran the action's own dist/index.js with Node.js, passing the same inputs the runner passes, against our test workspace with a throwaway bot token:

Step we ran	Result
chat.postMessage with the payload above	Posted. Outputs ok=true, ts, channel_id and time
A second step with thread_ts: set to the first ts	Posted as a thread reply
chat.update with ts: set to the first ts	Edited the message in place
Wrong channel ID, default errors: false	Exit code 0, output ok=false; channel_not_found appeared only in the debug log
Wrong channel ID, errors: true	Exit code 1, An API error occurred: channel_not_found
A payload line at the wrong indent	Exit code 1, Invalid input! Failed to parse contents of the provided payload



The bot had the chat:write.public scope as well as chat:write, so it posted to a public channel it had never joined. With only chat:write, invite it first. We deleted the messages and the test app afterwards.

Use if: always() to post on every run, and ${{ job.status }} in the text to say success or failure.

Option 2: incoming webhook

An incoming webhook posts to one channel, chosen when you create it. No channel ID or invite is needed.

• In your Slack app, turn on Incoming Webhooks, click Add New Webhook to Workspace, and pick the channel.
• Copy the URL, which looks like https://hooks.slack.com/services/T.../B.../..., into the repository secret SLACK_WEBHOOK_URL.

      - name: Post the build result to Slack
        if: always()
        uses: slackapi/slack-github-action@v4.0.0
        with:
          webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
          webhook-type: incoming-webhook
          payload: |
            text: "*${{ github.workflow }}*: ${{ job.status }}\n${{ github.event.head_commit.url }}"

A webhook cannot reply in threads or edit its message. For those, use Option 1. A third setting, webhook-type: webhook-trigger, starts a Slack Workflow Builder workflow instead of posting a message; ideas for those workflows are in Slack Workflow Builder examples.

Step-by-step setup of the webhook URL itself, including private channels and DMs, is in how to create a Slack webhook.

Option 3: curl, with no third-party action

Some organizations allow only GitHub's own actions. A run step with jq and curl, both installed on GitHub's Ubuntu runners, posts to an incoming webhook (the same call outside CI, in Python and Node too, is in Slack webhook curl example):

      - name: Post to Slack with curl
        if: failure()
        env:
          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
          STATUS: ${{ job.status }}
        run: |
          jq -n --arg text "$GITHUB_WORKFLOW on $GITHUB_REF_NAME: $STATUS $GITHUB_SERVER_URL/$GITHUB_REPOSITORY/actions/runs/$GITHUB_RUN_ID" '{text: $text}' |
            curl -sS --fail -X POST -H 'Content-type: application/json' --data @- "$SLACK_WEBHOOK_URL"

jq builds the JSON, so quotes in a branch name or commit message do not break it. --fail makes the step fail if Slack rejects the post. We ran the command outside GitHub with the same variables: jq printed {"text": "CI on main: failure https://github.com/acme/app/actions/runs/123"}, and a made-up webhook URL made curl exit with an error on Slack's 404, as it should.

Threads, updates and files

With a bot token, each step returns the message's ts as an output, so later steps can reply in a thread or edit it. Give the first step an id:

      - name: Announce the deploy
        id: deploy_message
        uses: slackapi/slack-github-action@v4.0.0
        with:
          method: chat.postMessage
          token: ${{ secrets.SLACK_BOT_TOKEN }}
          payload: |
            channel: ${{ secrets.SLACK_CHANNEL_ID }}
            text: "Deploy of ${{ github.sha }} started :eyes:"

      - run: ./deploy.sh

      - name: Reply in the thread
        uses: slackapi/slack-github-action@v4.0.0
        with:
          method: chat.postMessage
          token: ${{ secrets.SLACK_BOT_TOKEN }}
          payload: |
            channel: ${{ secrets.SLACK_CHANNEL_ID }}
            thread_ts: "${{ steps.deploy_message.outputs.ts }}"
            text: "Deploy finished :rocket:"

Swap the second step's method for chat.update and use ts: instead of thread_ts: to edit the first message in place. method: files.uploadV2 with channel_id, file and filename uploads a test report; it needs the files:write scope and uses the 3-step upload that replaced files.upload.

Option 4: the GitHub app for Slack

If you only want to know when workflows finish, the GitHub app for Slack needs no YAML. Install it from the Slack Marketplace, then in a channel run:

/github subscribe owner/repo workflows:{event:"push" branch:"main"}

It posts each workflow run and updates the message as jobs finish. It cannot send custom text; for that, use one of the options above.

Common errors

Secrets are not passed to workflows triggered by pull requests from forks, so the step fails there by design. Run it only on push or on pull requests from the same repository.

Long CI logs hit Slack text limits; the numbers and a split function are in Slack message character limit.

FAQ

What is the latest version of slack-github-action? v4.0.0, released 15 July 2026, commit dcb1066f776dd043e64d0e8ba94ca15cc7e1875d. It requires multi-line payload values to be indented.

How do I send a Slack notification only when a GitHub workflow fails? Add if: failure() to the Slack step. Use if: always() to post on every run.

Why is my Slack step green when nothing was posted? The errors input defaults to false, so a Slack error such as channel_not_found does not fail the step. Set errors: true.

Can I send a Slack message from GitHub Actions without a third-party action? Yes. Use curl with a Slack incoming webhook URL in a run step, with jq to build the JSON.