Comms
Email, messaging, voice and chat APIs for agents that talk to people.
JSON: /api/v1/directory.json (filter on category=comms)
Resend
Developer-focused email sending API with a free tier and official SDKs.
Free tierAPI keyTwilio
Programmable SMS, voice, WhatsApp and verification APIs used by many production systems.
PaidAPI keySlack API
Build bots and apps that read and post in Slack workspaces using the Web API and events.
Free tierOAuthTelegram Bot API
Free HTTP interface for creating Telegram bots, with tokens issued by BotFather.
FreeAPI keyDiscord Developer Platform
Bot and application APIs for building agents that live in Discord servers.
FreeOAuthSendGrid
Twilio's transactional and marketing email service with a REST API.
Free tierAPI keyPostmark
Transactional email with a reputation for fast, reliable delivery and clear logs.
PaidAPI keyMailgun
Email API for sending, receiving and parsing messages programmatically.
Free tierAPI keyAgentMail
Email inboxes created through an API specifically so agents can send and receive mail.
Free tierAPI keyVonage APIs
SMS, voice and messaging APIs from Vonage for global communications.
PaidAPI keyMicrosoft Graph
One API for Outlook mail, Teams, calendar and files across Microsoft 365.
FreeOAuthGmail API
Read, send and label Gmail messages on a user's behalf through OAuth.
FreeOAuthWhatsApp Business Platform
Meta's Cloud API for sending and receiving WhatsApp messages from businesses.
PaidAPI keyCloudflare Email Routing
Free custom-domain addresses that forward to an inbox or run through an Email Worker.
FreeAPI key