Agent skill

slack-webhook

Slack Webhook for posting messages. Use when user says "post to Slack", "Slack webhook", or "send Slack notification".

View SKILL.md on GitHub Repository
Stars 50
Forks 8

Install this agent skill to your Project

npx add-skill https://github.com/vm0-ai/vm0-skills/tree/main/slack-webhook

SKILL.md

Slack Incoming Webhook

Send messages to a Slack channel using Incoming Webhooks. No OAuth or bot setup required.

When to Use

  • Send notifications to a specific channel
  • CI/CD notifications, alerts, status updates
  • Quick integration without full Slack app setup

Prerequisites

bash
export SLACK_WEBHOOK_URL=https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXX

Get Webhook URL

  1. Create app: https://api.slack.com/apps → Create New App → From scratch
  2. Select Incoming Webhooks → Toggle On
  3. Click Add New Webhook to Workspace
  4. Select channel → Allow
  5. Copy Webhook URL

Usage

Simple Message

Write to /tmp/slack_request.json:

json
{
  "text": "Hello, world."
}

Then run:

bash
curl -X POST $(printenv SLACK_WEBHOOK_URL) -H "Content-type: application/json" -d @/tmp/slack_request.json

With Formatting

Write to /tmp/slack_request.json:

json
{
  "text": "*Bold* and _italic_ text"
}

Then run:

bash
curl -X POST $(printenv SLACK_WEBHOOK_URL) -H "Content-type: application/json" -d @/tmp/slack_request.json

With Link

Write to /tmp/slack_request.json:

json
{
  "text": "Check <https://example.com|this link>"
}

Then run:

bash
curl -X POST $(printenv SLACK_WEBHOOK_URL) -H "Content-type: application/json" -d @/tmp/slack_request.json

With Blocks (Rich Layout)

Write to /tmp/slack_request.json:

json
{
  "text": "New review submitted",
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "Danny left the following review:"
      }
    },
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "<https://example.com|Overlook Hotel>\n:star:\nDoors had too many axe holes."
      }
    }
  ]
}

Then run:

bash
curl -X POST $(printenv SLACK_WEBHOOK_URL) -H "Content-type: application/json" -d @/tmp/slack_request.json

With Fields

Write to /tmp/slack_request.json:

json
{
  "text": "Deployment status",
  "blocks": [
    {
      "type": "section",
      "fields": [
        {
          "type": "mrkdwn",
          "text": "*Environment:*\nProduction"
        },
        {
          "type": "mrkdwn",
          "text": "*Status:*\nSuccess"
        }
      ]
    }
  ]
}

Then run:

bash
curl -X POST $(printenv SLACK_WEBHOOK_URL) -H "Content-type: application/json" -d @/tmp/slack_request.json

Message Formatting

Syntax Result
*bold* bold
_italic_ italic
~strike~ strike
`code` code
\n newline
<URL|text> hyperlink
:emoji: emoji

Shell Escaping

Messages with ! may fail due to shell history expansion. Use heredoc:

bash
curl -s -X POST $(printenv SLACK_WEBHOOK_URL) -H "Content-type: application/json" -d @- << 'EOF'
{"text":"Deploy completed! :rocket:"}
EOF

Response

Success: ok (HTTP 200)

Errors:

  • invalid_payload - Malformed JSON
  • no_text - Missing text field
  • no_service - Webhook disabled or invalid
  • channel_not_found - Channel deleted
  • channel_is_archived - Channel archived
  • action_prohibited - Admin restriction

Limitations

  • One webhook = one channel only
  • Cannot override username or icon (set in app config)
  • Send only (no reading messages)
  • Cannot delete messages after posting
  • Rate limit: 1 message/second

For full API access, use the slack skill with Bot Token.

API Reference

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