Slack Webhook

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] ""

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

"SLACKWEBHOOKURL 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.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: aipcc-cicd
• Source: aipcc-cicd/claudio-skills
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.