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Channels

Slack

Post to Slack from your app with slack() — one webhook URL, zero config, the same shape as mail() and sms().

import { slack } from "postboi"

await slack({ title: "Deploy", message: "Finished in 42s" })
import { slack } from "postboi"

await slack({ title: "Deploy", message: "Finished in 42s" })

One env var and your app can talk to the team. The webhook URL carries the destination channel inside it, so there’s usually nothing to pass but the message.

Setup

The fast way: bunx postboi init --chat, pick Slack, choose Connect in the browser. Slack’s own consent screen asks which channel to post to, and the webhook lands in your env file without you ever seeing it. Signed in to Postboi, it also syncs to your team, so nobody else sets it up at all.

Or create an incoming webhook yourself and paste it:

# .env
SLACK_WEBHOOK_URL=https://hooks.slack.com/services/…
# .env
SLACK_WEBHOOK_URL=https://hooks.slack.com/services/…

Treat the URL as a secret — anyone holding it can post to your channel. It’s exactly the kind of credential team sync exists for.

Titles

title renders as bold mrkdwn above the message:

await slack({ title: "Build failed", message: "3 tests failing on main" })
await slack({ title: "Build failed", message: "3 tests failing on main" })

Posting to more than one channel

to overrides the webhook per message, so one app can serve several channels:

await slack([
	{ to: process.env.SLACK_ALERTS, message: "🔴 Checkout is down" },
	{ to: process.env.SLACK_DEPLOYS, message: "Deployed abc123" },
])
await slack([
	{ to: process.env.SLACK_ALERTS, message: "🔴 Checkout is down" },
	{ to: process.env.SLACK_DEPLOYS, message: "Deployed abc123" },
])

Each gets its own result — one failure never loses the rest.

Development posts for real

Unlike SMS, Slack is not intercepted in development: posting to your own channel while building is usually the point, costs nothing, and can be deleted. With no SLACK_WEBHOOK_URL configured, messages are captured by the dev inbox (or logged) instead of erroring.

Worth knowing

  • Slack replies to a failed post with a plain-text reason (no_service, invalid_payload) rather than JSON — that’s what lands in error.code.
  • In a multi-channel send(), the chat leg posts to whichever platform chat.provider names in your config. Your own code just calls slack().

Runnable example: examples/scripts/chat.ts posts to each platform in turn. The framework apps reach it through their POST /notify route — see the SvelteKit app.