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Rate Limiting

Exotel enforces rate limits on API requests and concurrent calls to ensure platform stability and fair usage across all accounts. Understanding these limits helps you design resilient integrations that handle throttling gracefully.

API Rate Limits​

Request Limits by Endpoint​

Endpoint CategoryRate LimitWindow
Voice API (make call, call details)200 requests/minutePer account
SMS API (send SMS, SMS details)200 requests/minutePer account
Bulk SMS API50 requests/minutePer account
WhatsApp API200 requests/minutePer account
ExoPhone API50 requests/minutePer account
Campaign API30 requests/minutePer account
User Management API50 requests/minutePer account
General GET endpoints300 requests/minutePer account
info

Rate limits shown are default values. Enterprise accounts may have custom limits. Check with your account manager for your account-specific limits.

Rate Limit Headers​

Exotel includes rate limit information in API response headers:

HeaderDescriptionExample
X-RateLimit-LimitMaximum requests allowed in the window200
X-RateLimit-RemainingRequests remaining in the current window150
X-RateLimit-ResetEpoch timestamp when the window resets1705312800

Rate Limit Exceeded Response​

When you exceed the rate limit, Exotel returns:

HTTP/1.1 429 Too Many Requests
Content-Type: application/json
Retry-After: 30

{
  "RestException": {
    "Status": 429,
    "Message": "Rate limit exceeded. Try again in 30 seconds.",
    "Code": "RATE_LIMIT_EXCEEDED"
  }
}

Concurrent Call Limits​

Concurrent call limits define the maximum number of simultaneous active calls on your account.

Default Limits by Plan​

PlanDefault Concurrent CallsMaximum (with upgrade)
Starter1025
Growth50200
EnterpriseCustom (starting at 100)1,000+

What Counts as a Concurrent Call​

ScenarioConcurrent Call Count
Single outbound call (one leg)1
Click-to-call (two legs)2
IVR call (caller navigating IVR)1
Call in queue (waiting for agent)1
Active call (parties talking)1 (or 2 for two-leg calls)
Call ringing (not yet answered)1

Concurrent Limit Exceeded​

When you hit the concurrent call limit:

  • New outbound API calls are rejected with an error
  • New inbound calls receive a busy signal or go to a configured fallback
  • Existing calls are NOT affected -- they continue normally

See Concurrent Calls for strategies to manage and scale your limits.

SMS Rate Limits​

Throughput Limits​

SMS TypeDefault Throughput
Transactional30 SMS/second
Promotional10 SMS/second
OTP30 SMS/second

Bulk SMS Limits​

ParameterLimit
Max recipients per API call100
Max SMS per minuteBased on throughput limits above
Max concurrent bulk jobs5 per account

Handling Rate Limits​

Retry Strategy with Exponential Backoff​

When you receive a 429 response, implement exponential backoff:

Attempt 1: Wait 1 second, then retry
Attempt 2: Wait 2 seconds, then retry
Attempt 3: Wait 4 seconds, then retry
Attempt 4: Wait 8 seconds, then retry
Attempt 5: Wait 16 seconds, then retry
Max retries: 5 (then fail and log)
tip

Always check the Retry-After header in the 429 response. It tells you exactly how many seconds to wait before retrying.

Request Queuing​

For high-volume integrations, implement a request queue:

  1. Place all API requests in a queue
  2. A worker processes requests from the queue at a controlled rate
  3. If a 429 response is received, the worker pauses and retries
  4. Failed requests are re-queued with a backoff delay

Rate Limit Monitoring​

Track your API usage to stay within limits:

MetricHow to Monitor
Requests per minuteTrack from your application logs
429 error rateMonitor from your error tracking system
Concurrent callsCheck via the Real-Time Dashboard
Remaining quotaRead X-RateLimit-Remaining headers

Requesting Higher Limits​

If your default limits are insufficient:

For API Rate Limits​

  1. Contact your account manager or raise a support ticket
  2. Provide details:
    • Which endpoints need higher limits
    • Expected request volume (requests per minute)
    • Business justification
  3. Rate limit increases are evaluated based on your plan and usage patterns

For Concurrent Call Limits​

  1. Navigate to Settings > Account > Concurrent Calls (or contact support)
  2. Request the desired concurrent call limit
  3. Provide:
    • Expected peak concurrent calls
    • Average call duration
    • Peak traffic hours

See Concurrent Calls for detailed scaling guidance.

Best Practices​

  1. Implement retries with backoff -- Never retry immediately after a 429; always wait
  2. Read rate limit headers -- Use X-RateLimit-Remaining to throttle proactively before hitting limits
  3. Batch when possible -- Use bulk endpoints (e.g., bulk SMS) instead of individual requests
  4. Cache API responses -- Cache call details and other read-heavy data to reduce API calls
  5. Use webhooks over polling -- Receive events via webhooks instead of polling the API for status updates
  6. Monitor your usage -- Set up alerts for high 429 error rates
  7. Design for limits -- Build your integration assuming limits exist; do not assume unlimited capacity
  8. Spread traffic evenly -- Avoid burst patterns; distribute API calls evenly over time

Troubleshooting​

IssuePossible CauseResolution
Frequent 429 errorsExceeding request rateImplement backoff and request queuing
Outbound calls failingConcurrent call limit reachedMonitor active calls; increase limit if needed
SMS not sendingSMS throughput limit reachedReduce send rate; use bulk endpoint
API slow during peaksApproaching rate limitsDistribute load; cache where possible
Inconsistent rate limitsMultiple API keys hitting same account limitRate limits are per-account, not per-key