The request names Slack, so Slack comes first: it offers a Web API and an @slack/web-api SDK, and its indexed actions include sending, me-messages and scheduling messages to a channel 111. Among alternatives, Mattermost can send messages to a channel and make custom API calls for self-hosted or air-gapped teams 919, Sonar Slack Notify posts Slack notifications for failed GitHub Checks 313, and Twilio sends messages over SMS, MMS, RCS and WhatsApp rather than Slack 1020.
- 1
Slack Web APIslack.comverified and signed
Slack is the AI work platform for team messaging; its Web API and @slack/web-api SDK let you post messages to a channel, share me-messages, and schedule messages 111.
official:API · Slack Web APISDK · @slack/web-api+210 community tools built for it
for agents: chat_postMessage · chat_meMessage · chat_scheduleMessage
- 2
Mattermostmattermost.comverified and signed
A self-hosted, private cloud or air-gapped team messaging platform whose indexed actions send a message to a channel and make custom API calls 919.
+20 community tools built for it
for agents: send_message · custom_api_call · mattermost/action-mattermost-notify
- 3
- 4
Twiliotwilio.comverified and signed
Programmable Messaging API that sends SMS, MMS, RCS and WhatsApp messages, not Slack messages 1020.
official:SDK · twiliolibrary · Twilioskill · twilio-send-messageSDK · twilio+21 community tools built for it
for agents: twilio-send-message · custom_api_call · api
Sources
- 1Slack | AI Work Platform & Productivity Toolsslack.com · read 2026-10-29
- 3AI Code Review & Verification Tools | Code Security | Sonarsonarsource.com · read 2026-10-29
- 9Mattermost | Operational and AI Sovereignty for Critical Infrastructure and National Securitymattermost.com · read 2026-10-29
- 10Docs: API Reference, Tutorials, and Integration | Twiliotwilio.com · read 2026-10-29
- 11Slack Web API: declares "chat_postMessage" (the record we read and signed)unfragile.ai · read 2026-10-24
- 13Slack Notify: declares "SonarSource/gh-action_slack-notify" (the record we read and signed)unfragile.ai · read 2026-10-24
- 19Mattermost (Activepieces): declares "send_message" (the record we read and signed)unfragile.ai · read 2026-10-24
- 20twilio-send-message: declares "twilio-send-message" (the record we read and signed)unfragile.ai · read 2026-10-24
For agents: the 10 actions behind this answer
chat_postMessage · Slack Web API verified and signed
Sends a message to a channel.
ai_alpha_search_messages · Slack AI Plugin verified and signed
Search for messages matching a query
· MEOK Slack Messaging website read, tools not yet checked
Start a source-backed conversation with MEOK. Read public evidence, keep a useful brief and reopen it later. Private AI staff and voice are not connected yet.
SonarSource/gh-action_slack-notify · Slack Notify verified and signed
GitHub Action to send Slack notifications for failed GitHub Checks
· slacking.biz website read, tools not yet checked
hashicorp/actions-slack-status · Slack Status Notification verified and signed
Slack Status Notification (replacement for circleci_slack_status orb).
· slackbuilds [Slackermedia Handbook] website read, tools not yet checked
· Slackware website read, tools not yet checked
Alien BOB's Slackware Linux and Slackware based projects mirror site.
· Slackware Linux Essentials website read, tools not yet checked
send_message · Mattermost (Activepieces) verified and signed
Send Message — Send a message to a Mattermost channel
Labels are the instruments' verdict and are never changed by ranking. Agents and robots get this same answer as JSON at /api/v1/find?q=…&answer=1 and through the MCP server.