Guides, tutorials and glossary
How to pick, set up and secure email, SMS, OTP and WhatsApp APIs, written for people building with AI tools. Prices and features come from the vendors' own pages and carry the date we checked them.
Guides
Vibe Coding Security Checklist (2026)
A vibe coding security checklist for Lovable, Bolt, Replit, v0 and Cursor apps: exposed API keys, Supabase RLS, OTP abuse, webhook signatures, MCP tokens.
Updated 21 October 2026
SMS OTP vs WhatsApp/Email/Voice 2026
SMS, WhatsApp, email or voice for one-time codes in the US, Brazil and Mexico: cost per code, NIST status, autofill, SMS pumping controls and fallback order.
Updated 15 October 2026
WhatsApp Business API Guide 2026: Access, Pricing, Setup
What the WhatsApp Business API is, how to get access directly or through a BSP, verification, template categories and per-message pricing incl. October 2026.
Updated 27 September 2026
Transactional Email in 2026: What It Is and How to Set It Up
Transactional email for developers: what counts, SPF, DKIM and DMARC setup, Gmail and Yahoo rules, webhooks, and provider prices checked in September 2026.
Updated 25 September 2026
A2P 10DLC Registration: 2026 Guide
10DLC registration step by step: brand, vetting, campaign, what reviewers reject, how long it takes, and fees at six SMS providers checked in September 2026.
Updated 24 September 2026
Evolution API vs WhatsApp Cloud API 2026: Ban Risk, Cost
Evolution API's WhatsApp Web mode vs Meta's Cloud API: what WhatsApp's terms say, ban risk, Brazil message rates vs self-hosting, and BSPs for Brazil.
Updated 25 September 2026
Tutorials
Send Email with Python via an API: Flask & FastAPI
Send email from Python through an API instead of SMTP: SDK and requests code, Flask and FastAPI routes, retries without duplicates, signed bounce webhooks.
Updated 6 November 2026
WhatsApp AI Agent: Connect an LLM to WhatsApp and SMS
Connect your AI agent to WhatsApp and SMS: signed webhooks, one-time processing, the 24-hour window, Meta's 2026 AI rules, opt-outs and a human handoff.
Updated 29 October 2026
React Email with Next.js: Send Email
Send email from a Next.js App Router app with React Email 6: build a template, preview it, render HTML and text, send from a server route, then swap providers.
Updated 17 October 2026
WhatsApp Cloud API Tutorial (2026)
Set up the WhatsApp Cloud API step by step: Meta app, permanent token, template send in curl and Node.js, signed webhooks, 24-hour replies and going live.
Updated 9 October 2026
Send Email from Lovable and Supabase
Send email from a Lovable app on Supabase: Lovable Emails, custom SMTP for auth mail, an Edge Function with the key in secrets, webhooks and 10k-email costs.
Updated 5 October 2026
Send Text Message API: Node & Python
Send SMS from Node.js or Python with Twilio or Telnyx: server-side keys, 10DLC, signed delivery webhooks, safe retries and US costs, checked September 2026.
Updated 1 October 2026
Toll-Free Number Texting Verification
Get a toll-free number verified for texting: required fields, opt-in proof, sample messages, review times, fees and rejection fixes at six SMS providers.
Updated 24 September 2026
WhatsApp Business Verification Steps
Meta business verification for WhatsApp API users: who needs it, documents for the US and Brazil, Security Center steps, display names, limits, rejections.
Updated 24 September 2026
Alternatives and comparisons
Amazon SES Alternatives (2026): 13 Email APIs Compared
Amazon SES alternatives ranked by our transactional email rating, with prices at 10,000 emails, free tiers, MCP, OAuth, webhook signing and idempotency keys.
Updated 24 September 2026
SendGrid Alternatives (2026): 13 Email APIs Ranked
SendGrid alternatives ranked by our transactional email rating: free plans, prices at 10k and 100k emails, MCP, OAuth and webhooks, checked 24 September 2026.
Updated 24 September 2026
Twilio Alternatives (2026): 15 SMS, OTP and WhatsApp APIs
Twilio alternatives ranked by our SMS rating, with OTP and WhatsApp places, US prices for 1,000 texts, Verify, MCP and OAuth, checked 24 September 2026.
Updated 25 September 2026
Articles
MCP OAuth for AI Agents: OAuth vs API Keys and PKCE
How MCP OAuth works in the 2026-07-28 spec (OAuth 2.1, PKCE, resource metadata), when an agent needs OAuth or an API key, and which messaging APIs offer it.
Updated 4 November 2026
Email API vs SMTP Relay: Which Should Your App Use?
Email API or SMTP relay? How each one sends, where each breaks (duplicate sends, blocked ports on AWS, Supabase and DigitalOcean) and which one your app needs.
Updated 2 November 2026
Email MCP Servers 2026: Resend, SendGrid, Mailgun, Postmark
Which email APIs have an official MCP server that can send: Resend, Mailgun, Postmark, Mailtrap and more. SendGrid's is docs-only. Auth, key scopes, safe setup.
Updated 27 October 2026
Free Email API Tiers Compared (2026)
Free email API and SMTP relay tiers from 13 providers, checked 24 September 2026: monthly and daily caps, card rules, trials, approval steps and upgrade costs.
Updated 25 October 2026
WhatsApp Business API Pricing 2026
Meta's per-message WhatsApp rates for the US, Brazil and Mexico, how providers add fees, costs at 1,000 and 10,000 messages and the October 2026 changes.
Updated 7 October 2026
SMS Sender ID Rules by Country 2026
Which SMS sender IDs work in 24 countries: alphanumeric support, sender ID registration, lead times and what carriers do with unregistered sender names.
Updated 24 September 2026
Use cases
Payment Reminder Message Templates: SMS, WhatsApp, Email
Payment reminder message templates for SMS, WhatsApp and email, when to send them, Stripe invoice events as triggers and how to stop once the invoice is paid.
Updated 8 November 2026
Text to Pay by SMS, WhatsApp, Email
Text to pay for developers: your PSP creates the link, you send it by SMS, WhatsApp or email, a signed webhook confirms payment. US, Brazil and Mexico rules.
Updated 19 October 2026
Troubleshooting
Glossary
One-Time Password (OTP): Meaning and How It Works
A one-time password (OTP) is a code that works once and expires in minutes: how HOTP, TOTP and random codes work, how long they last and what NIST allows.
Updated 31 October 2026
CPaaS Meaning: Communications APIs, Pricing and Vendors
CPaaS means cloud APIs for SMS, voice, WhatsApp, email and one-time codes: the building blocks, how pricing stacks up and how 27 providers compare by type.
Updated 25 September 2026
What Is llms.txt? Format, llms-full.txt and AI Crawlers
llms.txt is a proposed Markdown file that maps a site for AI agents: format, llms-full.txt, robots.txt differences, crawler support and which APIs publish one.
Updated 24 September 2026
What Is an MCP Server? Model Context Protocol Explained
An MCP server gives AI agents tools and data over the Model Context Protocol: local vs remote, OAuth 2.1 sign-in, official vs community servers and the risks.
Updated 25 September 2026
SMS Gateway: What It Is, How It Works, What It Costs
An SMS gateway links apps to mobile carriers: HTTP API vs SMPP, delivery receipts, sender registration and what 1,000 texts cost in the US, Brazil and Mexico.
Updated 25 September 2026
What Is SMTP? How It Works, Ports and Authentication
SMTP is the protocol that sends email from apps to relays and between servers: how a session works, reply codes, ports 25, 587 and 465, and SMTP AUTH.
Updated 25 September 2026
What Is a Webhook? Definition, Examples and Security
A webhook is an HTTP request an app sends to your URL when an event happens. How it differs from polling, how retries and HMAC signatures work, with examples.
Updated 24 September 2026