Send a Slack message

We have a collection of GitHub Actions that can be used to implement common Workflows to improve the efficiency of your projects. Alongside these Actions are also pre-configured Workflows that implement the most common of these, for your convenience.

View the innovation-shared-actions repository (internal).

Slack notification workflow

This is a GitHub Actions workflow that sends notifications to Slack channels. It supports posting a primary message and an optional threaded follow-up message. Repositories within the same GitHub organization can call this workflow to standardize Slack notifications across teams.

How it works

The Slack Notification workflow wraps our custom slack-message action, which calls the Slack API directly. It sends:

1. A primary Slack message to a specified channel
2. An optional threaded message using the timestamp of the first message

It calls Slack’s chat.postMessage API method under the hood. Read more at the Slack API docs.

Requirements

Repo must be in the same organization

This workflow consumes an organization-level secret. GitHub only allows access to shared workflow secrets if the calling repository is in the same GitHub org.

Add the Slack notification bot to your Slack channel

Slack will block messages unless the bot is a member of the channel.

To add the bot:

1. Open the Slack channel
2. Add “Notification Bot” to the channel
3. Ensure the bot appears in the channel’s integrations list

If you need to make changes to the Slack bot or need to access the key directly, reach out to Tech Ops so you can be added as a collaborator.

Required secret: SLACK_OAUTH_TOKEN

The workflow expects a secret named: SLACK_OAUTH_TOKEN (this is already installed)

This is configured as an organization secret, accessible to any repo using the workflow.

Inputs

The workflow accepts all the same inputs as the action (see below), minus token which is handled automatically via the org secret.

Name	Required	Type	Description
channel_id	Yes	string	Slack channel ID (ex: C09Q34G9HMX).
message	*	string	Main message posted to the channel. Required unless message_ts is provided.
message_ts	No	string	Timestamp of an existing message to update and/or reply to in thread.
thread_message	No	string	Optional threaded message.
username	No	string	Display name to post the main message as.
avatar_url	No	string	Avatar image URL for the main message. Takes priority over avatar_emoji.
avatar_emoji	No	string	Slack emoji for the main message avatar (e.g. :kangaroo:).
thread_username	No	string	Display name to post the threaded message as.
thread_avatar_url	No	string	Avatar image URL for the threaded message. Takes priority over thread_avatar_emoji.
thread_avatar_emoji	No	string	Slack emoji for the threaded message avatar.

Note

One or both of message or message_ts must be provided. When message_ts is provided without message, the action will thread a reply to the existing message instead of posting a new one. When both are provided, the main message’s content will be updated, and any provided thread_message will also be sent.

Caution

The username, avatar_url, thread_username and thread_avatar_url parameters give the ability to impersonate real users. This should only ever be done when the running of the workflow is triggered by the person themself—in other words, it should never be a surprise to someone that a Slack App is sending a message on their behalf.

Outputs

Name	Description
message_ts	Timestamp of the main message sent. Can be used to send later messages in a thread and/or update the main message’s content.

Using this workflow in your repository

Create a new workflow file, e.g. .github/workflows/notify.yml:

name: "Notify Slack"

on:
  workflow_dispatch: ## replace this with how you want to trigger the notification

jobs:
  notify-slack:
    uses: newjersey/innovation-shared-actions/.github/workflows/slack.yml@main
    with:
      channel_id: C09Q34G9HMX
      message: "Something cool happened!"
      thread_message: "And everything is great!" # optional
    secrets: inherit

Slack message action

If you find yourself limited by it, instead of using the above workflow you can use the underlying Action directly. This gives you a bit more composability for building more complex workflows.

How it works

The action handles:

1. Sending a primary message to a Slack channel
2. Updating an existing message (when message_ts is provided along with message)
3. Optionally sending a threaded reply using the timestamp from the first message
4. Returning the message timestamp for potential use in subsequent steps
5. Optionally impersonating a user by overriding the bot’s display name and avatar

Requirements

Slack OAuth Token

You’ll need access to a Slack OAuth token with the necessary permissions to post messages. Likely, the organization secret SLACK_OAUTH_TOKEN will be sufficient, if not, you’ll need to create another Slack Bot or request additional permissions for the existing one.

Bot must be added to the channel

Same requirement as the workflow - the Slack bot must be a member of the target channel.

Inputs

All inputs can alternatively be provided as CAPITAL_CASE environment variables (e.g., CHANNEL_ID, MESSAGE). Environment variables take priority over action inputs, which makes this action flexible for use in multi-step workflows where values are computed in earlier steps and written to $GITHUB_ENV.

Name	Required	Type	Description
channel_id	Yes	string	Slack channel ID (ex: C09Q34G9HMX).
message	*	string	Main message posted to the channel. Required unless message_ts is provided.
message_ts	No	string	Timestamp of an existing message to update and/or reply to in thread.
thread_message	No	string	Optional threaded message.
token	Yes	string	Slack OAuth token.
username	No	string	Display name to post the main message as.
avatar_url	No	string	Avatar image URL for the main message. Takes priority over avatar_emoji.
avatar_emoji	No	string	Slack emoji for the main message avatar (e.g. :kangaroo:). Ignored when avatar_url is set.
thread_username	No	string	Display name to post the threaded message as.
thread_avatar_url	No	string	Avatar image URL for the threaded message. Takes priority over thread_avatar_emoji.
thread_avatar_emoji	No	string	Slack emoji for the threaded message avatar. Ignored when thread_avatar_url is set.

Note

One or both of message or message_ts must be provided. When message_ts is provided without message, thread_message must be provided and the action will thread a reply to the existing message instead of posting a new one. When both are provided, the main message’s content will be updated, and any provided thread_message will also be sent.

Caution

The username, avatar_url, thread_username and thread_avatar_url parameters give the ability to impersonate real users. This should only ever be done when the running of the workflow is triggered by the person themself—in other words, it should never be a surprise to someone that a Slack App is sending a message on their behalf.

Outputs

Name	Description
message_ts	Timestamp of the main message sent. Can be used to send later messages in a thread and/or update the main message’s content.

Using this action in your repository

name: "Custom Slack Workflow"

on:
  workflow_dispatch:

jobs:
  custom-notification:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6

      - name: Send Slack message
        id: slack
        uses: newjersey/innovation-shared-actions/.github/actions/slack-message@main
        with:
          channel_id: C09Q34G9HMX
          message: "Build completed successfully!"
          thread_message: "All tests passed"
          token: ${{ secrets.SLACK_OAUTH_TOKEN }}

      - name: Use message timestamp
        run: |
          echo "Message sent at: ${{ steps.slack.outputs.message_ts }}"

Using environment variables instead of inputs

When your message content is computed dynamically (e.g., from a previous step), you can set environment variables instead of passing inputs directly:

- name: Build message
  run: |
    echo "MESSAGE=Deploy of ${{ github.sha }} succeeded" >> "$GITHUB_ENV"
    echo "CHANNEL_ID=C09Q34G9HMX" >> "$GITHUB_ENV"
    echo "TOKEN=${{ secrets.SLACK_OAUTH_TOKEN }}" >> "$GITHUB_ENV"

- name: Send Slack message
  uses: newjersey/innovation-shared-actions/.github/actions/slack-message@main

Impersonating a user

- name: Send as deploy author
  uses: newjersey/innovation-shared-actions/.github/actions/slack-message@main
  with:
    channel_id: C09Q34G9HMX
    message: "I just deployed to production!"
    username: "jviall"
    avatar_url: "https://avatars.githubusercontent.com/u/12345"
    thread_message: "Details in the thread"
    thread_username: "Deploy Bot"
    thread_avatar_emoji: ":rocket:"
    token: ${{ secrets.SLACK_OAUTH_TOKEN }}

References

• Slack notification workflow
• Slack message action
• Example notification implementation
• Example Slack notification
• Slack API: chat.postMessage
• Slack app (access required)