Slack

UpSlim sends Slack alerts using the chat.postMessage API with a Bot token. Messages use Block Kit with a colored border to distinguish DOWN, STILL DOWN, and RECOVERED states.

Setup

1. Create a Slack App

Go to api.slack.com/apps and create a new app From scratch.

2. Add Bot Token Scopes

In OAuth & Permissions → Scopes → Bot Token Scopes, add:

Scope	Required for
chat:write	Sending messages

3. Install to workspace

Click Install to Workspace. Copy the Bot User OAuth Token — it starts with xoxb-.

4. Invite the bot to the channel

In Slack, open the target channel and type:

/invite @your-bot-name

The bot must be a member of the channel before it can post.

5. Get the channel ID

Right-click the channel in Slack → Copy link or open channel details. The channel ID is a string like C0AR8F8BUDA. You can use either the ID or the channel name (#ops-alerts).

Configuration

alerting:
  - name: slack-ops
    type: slack
    token: ${SLACK_BOT_TOKEN}    # xoxb- token
    channel: "C0AR8F8BUDA"       # channel ID or "#channel-name"
    reminder_interval: 2h        # optional

Store your token as an environment variable and reference it with ${SLACK_BOT_TOKEN}.

Provider fields

Field	Type	Required	Description
name	string	yes	Reference name for monitors
type	slack	yes	Must be slack
token	string	yes	Bot token starting with xoxb-
channel	string	yes	Channel ID (C…) or name (#…)
reminder_interval	duration	no	Resend interval while still down

Message format

UpSlim sends Block Kit messages with a color-coded sidebar:

State	Color	Header
DOWN	🔴 Red #DD0000	service-name is DOWN
STILL DOWN	🟠 Orange #FF8C00	service-name is STILL DOWN
RECOVERED	🟢 Green #36A64F	service-name is RECOVERED

Each message includes monitor name, timestamp, response time, URL (HTTP), and the condition that failed.

Validation errors

UpSlim validates the Slack config at startup and exits immediately if:

• The token is empty
• The token does not start with xoxb- (user tokens starting with xoxp- are not supported)
• The channel is empty

Fatal error: Config error: Slack provider 'slack-ops': token must start with 'xoxb-' (Bot token)

Troubleshooting

channel_not_found — The bot has not been invited to the channel. Run /invite @bot-name in the channel.

not_authed — The token is invalid or expired. Regenerate it in the Slack app settings.

invalid_auth — The token format is wrong. Ensure it starts with xoxb-.