slack-webhook

name	slack-webhook
description	Post messages to Slack via incoming webhook URLs. Supports plain text and Slack Block Kit JSON.
compatibility	Requires SLACK_WEBHOOK_URL environment variable.
allowed-tools	Bash(*/slack-webhook/scripts/post-to-slack.sh *),Bash(*/tools/*/install.sh *)

Slack Webhook

Post messages to Slack channels via incoming webhook URLs. This is a notification-only skill — no reading or searching. For full Slack API access (fetch messages, search channels, threads), use the slack-utilities skill instead.

Prerequisites

Required:

• SLACK_WEBHOOK_URL - Slack incoming webhook URL (create one at https://api.slack.com/messaging/webhooks)
• curl - HTTP client (typically pre-installed)
• jq - JSON processor (install via tools/jq/install.sh)

Script: post-to-slack.sh

Usage:

${CLAUDE_SKILL_DIR}/scripts/post-to-slack.sh [--check] [--blocks] "<message_or_json>"

Flags:

• --check - Verify SLACK_WEBHOOK_URL is set without sending a message
• --blocks - Treat the argument as a Slack Block Kit JSON array instead of plain text

Environment Variables:

• SLACK_WEBHOOK_URL (required) - The incoming webhook URL

Examples

Plain text message

${CLAUDE_SKILL_DIR}/scripts/post-to-slack.sh "Build completed successfully"

Formatted text (Slack mrkdwn)

${CLAUDE_SKILL_DIR}/scripts/post-to-slack.sh "*Build Status:* :white_check_mark: Success\nVersion: \`3.2.3\`"

Block Kit JSON

${CLAUDE_SKILL_DIR}/scripts/post-to-slack.sh --blocks '[
  {
    "type": "header",
    "text": {"type": "plain_text", "text": "Release v3.2.3"}
  },
  {
    "type": "section",
    "text": {"type": "mrkdwn", "text": "*Status:* Deployed to production\n*Duration:* 12m 34s"}
  }
]'

Preflight check

${CLAUDE_SKILL_DIR}/scripts/post-to-slack.sh --check

Exit Codes

Code	Meaning
0	Success
1	Invalid parameters (missing message, missing env var, invalid JSON)
2	Webhook error (network failure or non-200 HTTP response)

Differences from slack-utilities

	slack-webhook	slack-utilities
Auth	SLACK_WEBHOOK_URL	SLACK_XOXC_TOKEN + SLACK_XOXD_TOKEN
Capabilities	Post only	Read, search, post, threads
Language	Bash (curl + jq)	Python (requests)
Dependencies	curl + jq	pip install requests
Use case	Simple notifications	Full Slack integration

Troubleshooting

"SLACK_WEBHOOK_URL not set" - Export the webhook URL: export SLACK_WEBHOOK_URL="https://hooks.slack.com/services/T.../B.../..."

HTTP 403/404 - The webhook URL may be invalid or revoked. Create a new one in your Slack workspace settings.

HTTP 400 with --blocks - The Block Kit JSON is malformed. Validate it at https://app.slack.com/block-kit-builder.

"invalid Block Kit JSON" - The argument passed with --blocks is not valid JSON. Ensure it's a JSON array of block objects.