GitHub PR notifications for Slack

Reusable GitHub Actions workflow that posts one Slack message per PR and keeps it updated as the PR moves through its lifecycle. The same message is edited in place so the channel stays tidy and always shows the current status.

How it works:

PR event	Slack message
Opened / Reopened / Ready for review	Posts Code Review Requested (author, branch, link).
Reviewer requests changes	Updates the message to Changes Requested (adds reviewer).
PR merged	Updates the message to Merged (adds merged-by).
PR closed (not merged)	Updates the message to Closed.
PR converted to draft	Removes the Slack message and the hidden timestamp comment.

So the channel sees a single, up-to-date line per PR instead of multiple separate notifications.

The workflow paginates through PR comments to find the hidden timestamp that links the Slack message to the PR, so it works for PRs with many comments (up to 10 pages of 100 comments).

Slack app setup

Before configuring the GitHub side you need a Slack bot token and the channel ID.

1. Create a Slack app (skip if you already have one)

1. Go to api.slack.com/apps and click Create New App → From scratch.
2. Give it a name (e.g. "PR Notifications") and pick your workspace.
3. Under OAuth & Permissions → Scopes → Bot Token Scopes, add chat:write.
4. Click Install to Workspace (or reinstall if you added scopes later) and authorize.
5. Copy the Bot User OAuth Token (xoxb-...) from the OAuth & Permissions page -- this is your SLACK_BOT_TOKEN.

2. Invite the bot to the channel

The bot must be a member of the channel it posts to, otherwise the Slack API returns not_in_channel.

• Open the target channel in Slack, then either:
  • Type /invite @YourBotName, or
  • Open Channel settings → Integrations → Add apps and add your bot.

3. Find the channel ID

Right-click the channel name (or open channel details) and choose Copy link. The ID is the last path segment (starts with C, e.g. C08B0BH8R99). You can also find it at the bottom of the About tab in channel details.

Using this workflow in your repository

1. Add the SLACK_BOT_TOKEN secret in your repo (Settings → Secrets and variables → Actions → Secrets tab). Store the Bot User OAuth Token (xoxb-...) you copied above.

2. Create a workflow file in your repo (e.g. .github/workflows/slack-pr-notify.yml) that calls this reusable workflow:

name: Notify Slack on PR
on:
  pull_request:
    types: [opened, reopened, ready_for_review, converted_to_draft, closed]
  pull_request_review:
    types: [submitted]
jobs:
  notify:
    permissions:
      contents: read
      pull-requests: write   # required to store Slack message timestamp in a PR comment
    uses: OWNER/github-pr-slack/.github/workflows/slack-pr-notification-reusable.yml@main
    with:
      slack_channel_id: 'C09HB1Q3J69'
      # Optional: wait for CI before posting (opt-in; supply your check names)
      enable_wait_for_ci: true
      required_checks: 'tests,lint,prettier'
    secrets:
      SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}

Replace OWNER with the GitHub org or user that hosts this repo (e.g. nicasio or my-org).

You can also use repository variables instead of literal values (e.g. slack_channel_id: ${{ vars.SLACK_CHANNEL_ID }}) so the same repo can drive the workflow from Settings → Variables:

    with:
      slack_channel_id: ${{ vars.SLACK_CHANNEL_ID }}
      enable_wait_for_ci: ${{ vars.SLACK_ENABLE_WAIT_FOR_CI == 'true' }}
      required_checks: ${{ vars.SLACK_REQUIRED_CHECKS }}

Inputs

Input	Required	Description
slack_channel_id	Yes	Slack channel ID (e.g. C00HB0Q0J00).
required_checks	No	Comma-separated CI check names to wait for. Only used when enable_wait_for_ci is true. If empty when wait is enabled, the workflow continues without waiting.
enable_wait_for_ci	No	Set to true to wait for CI checks to pass before posting. If false or omitted, the workflow posts to Slack immediately.

CI wait is opt-in. Omit enable_wait_for_ci and required_checks to post to Slack immediately. To wait for CI first, set enable_wait_for_ci: true and required_checks to your repo’s check names (comma-separated).

Secret

• SLACK_BOT_TOKEN (required): Slack Bot User OAuth Token with chat:write; the bot must be invited to the target channel.

Configuring this repo (caller workflow)

The caller workflow (.github/workflows/slack-notification.yml) reads all configuration from repository variables and secrets. Set them under Settings → Secrets and variables → Actions.

Important: GitHub has two separate tabs -- Secrets and Variables. The workflow uses vars.* for non-sensitive config and secrets.* for the token. Putting a value on the wrong tab will cause the job to be silently skipped or fail.

Secrets tab (Settings → Secrets and variables → Actions → Secrets):

Secret	Required	Description
SLACK_BOT_TOKEN	Yes	Bot User OAuth Token (xoxb-...) with chat:write scope.

Variables tab (Settings → Secrets and variables → Actions → Variables):

Variable	Required	Description
SLACK_CHANNEL_ID	Yes	Slack channel ID (e.g. C08B0BH8R99).
SLACK_ENABLE_WAIT_FOR_CI	No	Set to true to wait for CI before posting; omit or set to anything else to post immediately.
SLACK_REQUIRED_CHECKS	No	Comma-separated CI check names when SLACK_ENABLE_WAIT_FOR_CI is true. Omit or leave empty to continue without waiting for checks.

If SLACK_CHANNEL_ID is not set (or placed in Secrets instead of Variables), the notify job is silently skipped.