OpenClaw + Twilio: Build SMS and Voice AI Agents That Scale

SMS reaches people that apps don't. 98% open rate, no app install required, works on every phone made in the last 20 years. Pairing that channel with an OpenClaw AI agent creates a support or notification system that meets users exactly where they are.

This guide covers the complete setup — Twilio account configuration, OpenClaw gateway YAML, webhook routing, voice call handling, and the compliance requirements that trip up most first-time deployments. We'll get to the exact config in a moment, but first you need to understand the webhook flow — because getting this wrong causes silent message drops that are painful to debug.

How the OpenClaw-Twilio Integration Works

The architecture is straightforward. When someone texts your Twilio number, Twilio sends a POST request to your OpenClaw instance. OpenClaw processes the message through your configured agent, then returns a TwiML response that tells Twilio what to send back.

The critical constraint: Twilio expects an HTTP response within 15 seconds. If OpenClaw doesn't respond in time, Twilio retries — and you end up with duplicate messages. The fix is to acknowledge the webhook immediately and process the message asynchronously, which OpenClaw handles automatically when you enable async_mode: true.

Prerequisites

• OpenClaw v1.5.0 or later — Twilio voice support was added in v1.5
• A Twilio account with at least one active phone number
• A publicly reachable HTTPS endpoint (Twilio will not POST to HTTP or localhost)
• For US SMS at scale: a registered 10DLC campaign (see compliance section)

Twilio Account Setup

OpenClaw Gateway Configuration

SMS Channel Config

# config.yaml — Twilio gateway (SMS)
gateways:
  twilio:
    enabled: true
    account_sid: "${TWILIO_ACCOUNT_SID}"
    auth_token: "${TWILIO_AUTH_TOKEN}"
    validate_signature: true          # always true in production
    async_mode: true                  # acknowledge webhook instantly, process async
    queue_messages: true              # buffer bursts, prevents rate-limit drops

    sms:
      enabled: true
      from_number: "+15551234567"     # your Twilio number
      max_message_length: 1600        # split at 160 chars per segment automatically
      media_handling: download        # download | url_passthrough | ignore
      fallback_message: "We received your message and will respond shortly."

    channels:
      - sms

Voice Channel Config

    voice:
      enabled: true
      speech_model: "phone_call"      # Twilio speech recognition model
      tts_voice: "Polly.Joanna"       # AWS Polly via Twilio
      tts_language: "en-US"
      gather_timeout: 5               # seconds to wait for speech input
      max_call_duration: 600          # 10 minutes max, adjust as needed
      transcription: true             # store transcripts in OpenClaw logs
      fallback_twiml: |
        <Response>
          <Say>Sorry, I encountered an error. Please try again later.</Say>
          <Hangup/>
        </Response>

Webhook Configuration and Testing

After updating your config, restart OpenClaw and verify the gateway starts correctly:

$ openclaw restart && openclaw logs --tail 20 --gateway twilio

[2025-02-17 11:30:01] INFO  Twilio gateway: SMS enabled on /openclaw/twilio/sms
[2025-02-17 11:30:01] INFO  Twilio gateway: Voice enabled on /openclaw/twilio/voice
[2025-02-17 11:30:01] INFO  Signature validation: active
[2025-02-17 11:30:01] INFO  Async mode: enabled, queue worker started

Text your Twilio number with a simple "Hello" and watch the logs. A successful flow looks like this:

[2025-02-17 11:31:12] INFO  Twilio: inbound SMS from +15559876543
[2025-02-17 11:31:12] INFO  Signature validated: OK
[2025-02-17 11:31:12] INFO  Webhook acknowledged (12ms)
[2025-02-17 11:31:14] INFO  Agent: response generated (1.9s)
[2025-02-17 11:31:14] INFO  Twilio: outbound SMS sent to +15559876543

That 12ms acknowledgment time is what keeps Twilio happy. The actual agent response comes 1.9 seconds later via the outbound API — the user gets a reply, Twilio never times out, and nothing drops.

Scaling for High Volume

Twilio's SMS API has rate limits: 1 message per second for long codes, 100/second for short codes, and 10/second for toll-free numbers. OpenClaw's message queue handles traffic above these limits by batching outbound messages and respecting the per-number rate limit automatically.

For deployments above 10,000 SMS/day, consider these additional config settings:

• Multiple Twilio numbers — configure an array of from_numbers and OpenClaw round-robins across them, multiplying your effective throughput
• Dedicated short code — 100 messages/second throughput, required if you're running any kind of campaign messaging at volume
• Queue persistence — set queue_backend: redis to persist the message queue across restarts; in-memory queues lose messages on restart
• Horizontal scaling — run multiple OpenClaw instances behind a load balancer; the Twilio gateway is stateless and scales linearly

Compliance: Opt-Out and 10DLC

This is where most teams cut corners and pay for it later. US carriers can block your Twilio number permanently if you violate messaging regulations.

The non-negotiables as of early 2025:

• 10DLC registration — all A2P (application-to-person) SMS in the US must use registered 10-digit long codes. Register your brand and campaign in Twilio Console. Takes 1–3 business days.
• STOP/UNSUBSCRIBE handling — Twilio handles standard opt-out keywords at the carrier level automatically. Never try to intercept or override these in your OpenClaw agent.
• Opt-in records — you must have documented consent before sending marketing messages. OpenClaw can log first-contact events, but the consent collection itself happens before a user texts you.
• Message frequency disclosure — your first-contact auto-reply must disclose message frequency and that standard rates apply if you're running any campaign messaging.

Common Mistakes

Every one of these has been reported in the OpenClaw community forum. Don't learn them the hard way.

• Hardcoded Auth Token in config.yaml — committed to git, rotated too late, compromised. Always use ${TWILIO_AUTH_TOKEN}.
• Signature validation disabled — your webhook endpoint is publicly accessible. Anyone can POST fake messages to your agent without validation enabled.
• Async mode off at volume — works fine in testing (one message at a time), breaks under real load when multiple users text simultaneously and Twilio starts timing out.
• In-memory queue with no persistence — a server restart during peak hours drops every queued message. Set queue_backend: redis for any production deployment.
• Skipping 10DLC registration — your messages go through initially, then carrier filtering kicks in 2–3 weeks later and deliverability drops to near zero. Register before launch.

Frequently Asked Questions

Does OpenClaw support Twilio voice calls as well as SMS?

Yes. Set channel: voice in your Twilio gateway block to handle inbound and outbound calls. OpenClaw converts speech to text via Twilio's transcription pipeline, processes it through your agent, and returns synthesized voice responses using TwiML. Both SMS and voice can run simultaneously under the same Twilio account.

How much does running OpenClaw with Twilio cost?

Twilio charges per SMS segment (roughly $0.0079 outbound in the US) and per call minute. OpenClaw itself has no per-message fee. The main cost driver is Twilio usage volume plus your AI model costs. A typical support bot handling 1,000 SMS conversations per day runs $20–$60/month in Twilio fees at US rates.

Can I use an existing Twilio number with OpenClaw?

Yes. Any Twilio phone number can be routed to OpenClaw by pointing the number's webhook URL to your OpenClaw instance. You don't need to buy a new number — update the webhook settings on your existing number in the Twilio console to point to your openclaw/twilio endpoint.

What happens if my OpenClaw instance goes down during an SMS conversation?

Twilio will retry the webhook delivery up to 3 times over 15 minutes. Enable OpenClaw's message queue with queue_messages: true and configure a fallback reply in fallback_message — users get an immediate acknowledgment while the agent recovers, preventing silent failures during brief outages.

How do I handle opt-out keywords like STOP and UNSUBSCRIBE?

Twilio handles STOP, HELP, and UNSUBSCRIBE automatically at the carrier level — OpenClaw never sees those messages. For custom opt-out flows, add keyword rules to your OpenClaw agent config. Attempting to override Twilio's native opt-out handling is against carrier regulations and will get your number flagged.

Can OpenClaw send proactive SMS messages, not just respond?

Yes. Use OpenClaw's outbound trigger API to push SMS messages through Twilio without a user initiating the conversation. Configure outbound: true in your gateway block and call the /api/trigger/sms endpoint with the recipient number and message payload. Requires the recipient to have previously opted in.

Does the OpenClaw Twilio gateway support WhatsApp through Twilio?

Twilio's WhatsApp Business API can be routed through the same OpenClaw Twilio gateway. Set channel: whatsapp alongside channel: sms to handle both. Note that WhatsApp through Twilio requires separate Meta business verification — the gateway config is identical but the onboarding process takes 1–5 business days.