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
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 24 September 2026
Tutorials
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 24 September 2026
Articles
Glossary
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 24 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 24 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 24 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 24 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