twilio-debugging-observability

Overview

Twilio provides several layers of debugging and observability: the Console Debugger for interactive troubleshooting, the Monitor REST API for programmatic alert queries, Event Streams for real-time error streaming, and status callbacks for per-resource delivery tracking. This skill covers the systematic approach to diagnosing issues and setting up production monitoring.

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Prerequisites

• Twilio account with TWILIO_ACCOUNT_SID and TWILIO_AUTH_TOKEN -- see twilio-iam-auth-setup
• SDK: pip install twilio requests / npm install twilio
• For Event Streams: a publicly accessible HTTPS endpoint or AWS Kinesis stream

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Quickstart

Check for recent errors on your account using the Monitor Alerts API.

Python

import os
from twilio.rest import Client

client = Client(os.environ["TWILIO_ACCOUNT_SID"], os.environ["TWILIO_AUTH_TOKEN"])

alerts = client.monitor.alerts.list(log_level="error", limit=10)
for alert in alerts:
    print(f"{alert.date_created}: [{alert.error_code}] {alert.alert_text}")

Node.js

const twilio = require("twilio");
const client = twilio(process.env.TWILIO_ACCOUNT_SID, process.env.TWILIO_AUTH_TOKEN);

const alerts = await client.monitor.alerts.list({ logLevel: "error", limit: 10 });
alerts.forEach(a => {
    console.log(`${a.dateCreated}: [${a.errorCode}] ${a.alertText}`);
});

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Key Patterns

1. Systematic Debugging Workflow

When something fails, work through these layers in order:

1. Check status callbacks FIRST
   (Did your endpoint receive delivery/call status? What error code?)
   |
2. Check the resource directly via REST API
   (GET /Messages/{sid} or /Calls/{sid} — current state + error_code)
   |
3. Check number reputation / sender registration
   (Is the number spam-flagged? Is A2P 10DLC registered? Toll-free verified?)
   |
4. Check the Console Debugger for webhook/TwiML errors
   (Console > Monitor > Errors — shows HTTP request/response details)
   |
5. Check your webhook endpoint
   (Is it reachable? Responding within 15s? Returning valid TwiML/200?)
   |
6. Query Monitor Alerts API or Event Streams
   (For patterns across many messages/calls, or historical analysis)

Why status callbacks first: Status callbacks tell you the exact error code for the specific message or call that failed. The Console Debugger aggregates errors across your account and may not surface the one you're looking for. Start specific, then broaden.

Number reputation checklist:

• SMS 30007 (carrier filtering) → Check A2P 10DLC registration status, content for spam triggers
• SMS 30034 → Sender not registered for A2P 10DLC — register brand + campaign
• Calls going to voicemail / "Spam Likely" → Check STIR/SHAKEN attestation, Voice Integrity status (see twilio-numbers-senders)
• Toll-free SMS blocked → Check toll-free verification status

Rule of thumb: If status callbacks show delivered but the user says they didn't receive it, the issue is on the carrier/device side (not Twilio). If the Console Debugger shows no errors at all, the problem is in your application (webhook, TwiML, business logic).

2. Console Debugger

The Console Debugger shows errors and warnings for your account in real time.

Each entry includes:

• The exact error or warning that occurred
• Potential causes and suggested solutions
• The full HTTP request and response for the associated webhook

Configure a Debugger webhook for real-time alerting:

Console > Monitor > Logs > Debugger > (gear icon) > set Callback URL

Debugger webhook POST parameters:

Parameter	Description
Sid	Debugger event identifier
AccountSid	Account that generated the event
Level	Error or Warning
Timestamp	ISO 8601 time
Payload	JSON: resource_sid, error_code, more_info, webhook (full request/response)

Python (Flask) -- debugger webhook handler

import json, os
from flask import Flask, request
from twilio.request_validator import RequestValidator

app = Flask(__name__)
validator = RequestValidator(os.environ["TWILIO_AUTH_TOKEN"])

@app.route("/debugger", methods=["POST"])
def debugger_event():
    sig = request.headers.get("X-Twilio-Signature", "")
    if not validator.validate(request.url, request.form, sig):
        return "Forbidden", 403
    level = request.form.get("Level")
    payload = json.loads(request.form.get("Payload", "{}"))
    error_code = payload.get("error_code")
    resource_sid = payload.get("resource_sid")
    msg = payload.get("more_info", {}).get("msg", "")
    print(f"[{level}] Error {error_code} on {resource_sid}: {msg}")
    return "", 204

Node.js (Express) -- debugger webhook handler

const express = require("express");
const twilio = require("twilio");
const app = express();
app.use(express.urlencoded({ extended: false }));

app.post("/debugger", (req, res) => {
    const valid = twilio.validateRequest(
        process.env.TWILIO_AUTH_TOKEN,
        req.headers["x-twilio-signature"],
        `https://${req.headers.host}${req.originalUrl}`,
        req.body
    );
    if (!valid) return res.status(403).send("Forbidden");
    const payload = JSON.parse(req.body.Payload || "{}");
    const { error_code, resource_sid } = payload;
    const msg = payload.more_info?.msg || "";
    console.log(`[${req.body.Level}] Error ${error_code} on ${resource_sid}: ${msg}`);
    res.sendStatus(204);
});

3. Monitor Alerts API

The Monitor REST API (monitor.twilio.com/v1/Alerts) provides programmatic access to error and warning logs. Individual alert instances include the full HTTP request and response data.

Python -- query alerts with date filtering

from datetime import datetime, timedelta

# Alerts from the last 24 hours
start = datetime.utcnow() - timedelta(days=1)
alerts = client.monitor.alerts.list(
    start_date=start,
    log_level="error",
    limit=50
)

for alert in alerts:
    print(f"{alert.date_created} [{alert.error_code}]")
    # Fetch full details including HTTP request/response
    detail = client.monitor.alerts(alert.sid).fetch()
    print(f"  Request URL: {detail.request_url}")
    print(f"  Response body: {detail.response_body}")

Node.js -- query alerts with date filtering

const startDate = new Date(Date.now() - 24 * 60 * 60 * 1000);
const alerts = await client.monitor.alerts.list({
    startDate,
    logLevel: "error",
    limit: 50,
});

for (const alert of alerts) {
    console.log(`${alert.dateCreated} [${alert.errorCode}]`);
    const detail = await client.monitor.alerts(alert.sid).fetch();
    console.log(`  Request URL: ${detail.requestUrl}`);
    console.log(`  Response body: ${detail.responseBody}`);
}

Retention: Enterprise accounts: 13 months. Free accounts: 30 days.

4. Monitor Events API

The Events resource (monitor.twilio.com/v1/Events) tracks all changes to Twilio resources -- phone number provisioning, account settings, recording access, API key creation, and more.

Python -- audit recent account changes

events = client.monitor.events.list(limit=20)
for event in events:
    print(f"{event.event_date}: {event.event_type}")
    print(f"  Resource: {event.resource_type} ({event.resource_sid})")
    print(f"  Actor: {event.actor_type} ({event.actor_sid}) from {event.source_ip_address}")

Each event captures: event type, resource, actor (who triggered it), source (API / Console / Twilio admin), and IP address.

Use cases:

• Audit who changed a phone number's webhook URL
• Track API key creation and deletion
• Detect unexpected configuration changes
• Feed events into a SIEM for security monitoring

5. Event Streams for Error Log Streaming

For production monitoring, stream errors to your infrastructure in real time using Event Streams. The Twilio SDK does not wrap Event Streams -- use requests / fetch directly.

Python -- set up error log streaming to a webhook

import os, requests

account_sid = os.environ["TWILIO_ACCOUNT_SID"]
auth_token = os.environ["TWILIO_AUTH_TOKEN"]

# Step 1: Create a webhook sink
sink = requests.post(
    "https://events.twilio.com/v1/Sinks",
    auth=(account_sid, auth_token),
    data={
        "Description": "Error monitoring sink",
        "SinkType": "webhook",
        "SinkConfiguration": '{"destination": "https://yourapp.com/twilio-errors", "method": "POST"}'
    }
).json()

# Step 2: Subscribe to error log events
subscription = requests.post(
    "https://events.twilio.com/v1/Subscriptions",
    auth=(account_sid, auth_token),
    data={
        "Description": "Error log subscription",
        "SinkSid": sink["sid"],
        "Types": '[{"type": "com.twilio.error-logs.error.logged"}]'
    }
).json()

print(f"Sink: {sink['sid']}, Subscription: {subscription['sid']}")

Sink types: webhook, kinesis, segment

Useful event types for observability:

Event type	Description
com.twilio.error-logs.error.logged	All errors and warnings on account
com.twilio.messaging.message.delivered	Message delivered successfully
com.twilio.messaging.message.undelivered	Message delivery failed
com.twilio.voice.insights.call-summary	Post-call quality and status summary

6. Status Callback Monitoring

Status callbacks are the most granular observability mechanism -- they fire for individual resource state changes.

Message delivery tracking:

# Attach when sending
message = client.messages.create(
    to="+15558675310", from_="+15017122661", body="Hello!",
    status_callback="https://yourapp.com/msg-status"
)

Call lifecycle tracking:

call = client.calls.create(
    to="+15558675310", from_="+15017122661",
    url="https://yourapp.com/voice",
    status_callback="https://yourapp.com/call-status",
    status_callback_event=["initiated", "ringing", "answered", "completed"]
)

Recording completion tracking:

# In TwiML
response = VoiceResponse()
response.record(
    recording_status_callback="https://yourapp.com/recording-status",
    recording_status_callback_event="completed absent failed"
)

Recording status values: in-progress, completed, absent, failed. The RecordingUrl is available when status is completed.

7. Debugging Webhooks

When Twilio can't reach your webhook or receives an error, the problem is often in your infrastructure.

Common causes and fixes:

Symptom	Likely cause	Fix
Error 11200 in Debugger	Webhook URL returned non-200 / unreachable	Verify endpoint is live: curl -I https://yourapp.com/sms
Error 11205	HTTP connection failure (port closed, refused, firewall)	Verify server is running and port is open: curl -I https://yourapp.com/sms
Error 12100	TwiML document could not be parsed	Check for debug output, BOM characters, or malformed XML
Parameters missing after redirect	HTTP 301/302 strips POST body	Fix URL to avoid redirect (add/remove www., use HTTPS directly)
Webhook works locally but not deployed	Tunnel expired or firewall	Use curl from an external host to test
Intermittent failures	ngrok session expired / recycled	Deploy to a stable host for anything beyond quick tests

Test webhooks manually:

# Simulate an inbound SMS webhook
curl -X POST https://yourapp.com/sms \
  -d "From=+15551234567" \
  -d "To=+15559876543" \
  -d "Body=Test message" \
  -d "MessageSid=SM00000000000000000000000000000000"

Browser testing: Visit your webhook URL in Firefox -- it highlights XML errors in the response.

8. Common Error Codes

Code	Name	Cause	Fix
11200	HTTP retrieval failure	Twilio cannot reach your webhook URL	Check URL, DNS, firewall, SSL cert
11205	HTTP connection failure	Webhook endpoint refused connection	Verify server is running and port is open
11751	Media download failure	MMS media URL unreachable	Check media URL accessibility
12100	Document parse failure	TwiML is not valid XML	Validate XML; remove debug output
12200	Schema compliance failure	TwiML verbs/attributes are invalid	Check TwiML reference for correct syntax
20003	Authentication error	Invalid Account SID or Auth Token	Verify credentials in environment
21211	Invalid To number	Number not in E.164 format	Use + country code + number
21608	Unverified number (trial)	Trial accounts can only send to verified numbers	Verify number or upgrade account
30003	Unreachable destination	Carrier cannot deliver message	Check number validity; retry later
30006	Landline or unreachable	Destination is a landline	Use voice channel instead
30007	Carrier filtering	Message filtered by carrier	Review content; register for A2P 10DLC
30008	Unknown error	Carrier returned generic error	Retry; contact support if persistent

Full error reference: https://www.twilio.com/docs/api/errors

9. Querying Resource State Directly

When you need the current state of a message or call (not waiting for a callback):

Python

# Check message delivery status
message = client.messages("SMxxxxxxxxxx").fetch()
print(f"Status: {message.status}, Error: {message.error_code}")

# Check call status
call = client.calls("CAxxxxxxxxxx").fetch()
print(f"Status: {call.status}, Duration: {call.duration}")

Node.js

const message = await client.messages("SMxxxxxxxxxx").fetch();
console.log(`Status: ${message.status}, Error: ${message.errorCode}`);

const call = await client.calls("CAxxxxxxxxxx").fetch();
console.log(`Status: ${call.status}, Duration: ${call.duration}`);

10. CLI Debugging

The Twilio CLI supports debug logging:

# Verbose output for any CLI command
twilio api:core:messages:list --limit 5 -l debug

# Log levels: debug, info, warn, error

Debug output goes to stderr, so you can pipe normal output while still seeing diagnostics.

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Monitoring Checklist

Set up before going to production:

What to monitor	How	Alert threshold
Webhook errors	Debugger webhook or Event Streams (com.twilio.error-logs.error.logged)	Any error
Message delivery failures	Status callback failed/undelivered	> 2% failure rate
Call completion rate	Status callback completed vs total	< 95% completion
Webhook response time	Your APM (DataDog, New Relic)	p95 > 5 seconds
429 rate limit hits	Count in your backoff handler	> 5% of requests
Account configuration changes	Monitor Events API	Any unexpected change
Recording failures	Recording status callback failed/absent	Any failure

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CANNOT

• Cannot fetch more than 10,000 alerts per request — Use date range filters for large accounts
• Cannot get full HTTP request/response from alert list — Only available when fetching a single alert by SID
• Cannot combine multiple filters on Events API — One additional field (ResourceSid, ActorSid, SourceIpAddress) plus date range per request
• Cannot delete an Event Streams sink before its subscription — Must delete the subscription first
• Cannot guarantee status callback delivery or order — Best-effort. Use composite keys for idempotency.
• Cannot rely on a static error code list — New error codes are added without notice. Always link to the full reference rather than hardcoding.

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Next Steps

• Webhook architecture: twilio-webhook-architecture
• Scale webhook handling: twilio-reliability-patterns
• Compliance monitoring: twilio-compliance-traffic
• Credential security: twilio-iam-auth-setup