Twilio

Programmable communications platform: SMS, MMS, WhatsApp, voice, email (via SendGrid). The default low-level API for custom SMS builds, transactional messaging, and B2B SaaS embedding SMS into products.

Capabilities

Authentication

• Type: Basic auth with Account SID + Auth Token (or API Key SID + Secret)
• Header: Authorization: Basic base64(AccountSID:AuthToken)
• Get credentials: https://console.twilio.com → Account Info
• Recommendation: Use API Keys (revocable, scoped) for production rather than the master Auth Token

Common Agent Operations

Send SMS

POST https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Messages.json

To=+15551234567
From=+15559876543
Body=Hello from Twilio

Send MMS

POST https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Messages.json

To=+15551234567
From=+15559876543
Body=Check this out
MediaUrl=https://example.com/image.jpg

List messages

GET https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Messages.json?PageSize=50

Get message status

GET https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Messages/{MessageSid}.json

Status values: queued, sending, sent, delivered, undelivered, failed.

List phone numbers

GET https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/IncomingPhoneNumbers.json

Buy a phone number

POST https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/IncomingPhoneNumbers.json

PhoneNumber=+15559876543

Configure webhook for inbound messages

POST https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/IncomingPhoneNumbers/{Sid}.json

SmsUrl=https://your-app.com/sms-webhook
SmsMethod=POST

Inbound SMS POSTs to the webhook with: From, To, Body, MessageSid, NumMedia, etc.

A2P 10DLC registration (US)

# Create brand
POST https://messaging.twilio.com/v1/a2p/BrandRegistrations

CustomerProfileBundleSid=...
A2PProfileBundleSid=...

# Create campaign
POST https://messaging.twilio.com/v1/Services/{ServiceSid}/Compliance/Usa2p

BrandRegistrationSid=...
Description=...
MessageSamples[]=Sample text 1
MessageFlow=Opt-in flow description
UseCase=MARKETING

Most workflows are clearer in the Console UI. Programmatic registration is for high-scale platforms managing many brands.

API Pattern

REST + form-encoded request bodies (not JSON for most endpoints). Resources nested under Account: /Accounts/{AccountSid}/.... Pagination via Page, PageSize, NextPageUri.

Key Concepts

• Messaging Service: virtual sender container; load-balances across multiple numbers, handles A2P registration grouping
• Sticky Sender: same recipient always receives from the same number within a service
• Geo-Match: route to a number matching the recipient's country/region
• Status Callback: webhook fired on every delivery state change
• Carrier Lookup: pre-send check for line type (mobile, landline, VoIP) — costs ~$0.005

Pricing

• US 10DLC SMS: $0.0079/msg
• US toll-free SMS: $0.0079/msg
• US short code SMS: $0.0079/msg + $1,000/mo lease
• MMS: ~$0.02
• Carrier surcharges (~$0.005 US 10DLC)
• A2P 10DLC: ~$15 brand + $10/mo per campaign
• Phone number rental: $1.15/mo (10DLC) to $2/mo (toll-free)

Rate Limits

• Default: 1 msg/sec on long codes (10DLC trust score raises this to 4–100+)
• Short code: 100+ msg/sec
• Messaging Services throttle automatically
• Carrier filtering applies above contracted throughput

When to Use

• Building custom SMS flows into a product (B2B SaaS, mobile apps)
• Transactional and auth SMS (OTPs, alerts, notifications)
• Multi-channel orchestration (SMS + voice + WhatsApp)
• High-volume programmable messaging
• When you need full control and minimal abstraction
• Backing store for Customer.io / Segment / other orchestration layers

When NOT to Use

• DTC ecom marketing flows — use Klaviyo, Postscript, or Attentive (better tooling for cart recovery, segments, A/B tests)
• If you don't want to handle compliance plumbing — Twilio gives you primitives, not policy
• Marketing UI for non-technical users — there isn't one

Relevant Skills

• sms
• emails (transactional sister product via SendGrid)
• onboarding (post-signup SMS milestones)