Best SMS API providers for compliant texting
7 APIs comparedVendor docs read 2026-10-22
For the developer or ops lead wiring texting into a product: which CPaaS providers handle STOP and HELP for you, which register 10DLC campaigns and toll-free numbers by API, and which compliance jobs stay in your own code whichever one you pick. We read each API's own documentation on 2026-10-22; every status names the page it came from. More side-by-sides sit in the comparisons index.
Verdict by use case
Best overall
The only API here whose docs hold a marketing text back during federal and state quiet hours and keep consent records with a date and source. 10DLC, toll-free verification and daily log exports are covered too; the toolkit works on US English SMS only.
Best for catching plain-language opt-outs
AI opt-out detection treats a reply like "please stop texting me" as a STOP, and the opt-out list can be read by API. Quiet hours stay in your code: scheduled sends go out on UTC.
Best for teams already on AWS
Opt-out lists fill themselves on STOP and are readable and writable by API, registrations are API resources, and delivery events land in your own CloudWatch, Firehose or SNS.
Seven APIs, eight requirements
The first five rows are the site's texting rows an API can act on; the last three are API rows a developer asks about first: toll-free verification in code, an opt-out list you can read, and logs you can take away. Registration itself is covered in the Registration pillar and in what 10DLC is. "Our pick" marks the best-overall verdict.
| Requirement | Our pickTwilio | Telnyx | Plivo | Vonage | Bandwidth | Sinch | AWS End User Messaging SMS |
|---|---|---|---|---|---|---|---|
| Honours STOP and plain-language revocation automatically | No | Yes | No | Check with the vendor | No | No | Check with the vendor |
| HELP auto-reply | Yes | Yes | Yes | Yes | Check with the vendor | Check with the vendor | Yes |
| 10DLC brand and campaign registration in-product | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
| Quiet-hours window by the recipient's time zone | Yes | No | Check with the vendor | Check with the vendor | Check with the vendor | Check with the vendor | Check with the vendor |
| Records opt-in with a timestamp and the number | Yes | Check with the vendor | No | Check with the vendor | No | Check with the vendor | Check with the vendor |
| Toll-free verification submitted by API | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
| Opt-out list readable by API | No | Yes | Check with the vendor | Check with the vendor | No | Yes | Yes |
| Message logs exportable in bulk | Yes | Yes | Yes | Yes | Yes | Check with the vendor | Yes |
- Honours STOP and plain-language revocation automatically
- The FCC rule names seven reply words and also counts any reply a reasonable person reads as a revocation.47 CFR § 64.1200(a)(10)
- HELP auto-reply
- CTIA's confirmation calls for customer care contact details or HELP instructions.CTIA Messaging Principles and Best Practices (May 2023), 5.1.2.1
- 10DLC brand and campaign registration in-product
- US carriers route business texts on local numbers through registered brands and campaigns.
- Quiet-hours window by the recipient's time zone
- Telephone solicitations are barred before 8 a.m. or after 9 p.m. local time at the called party's location.47 CFR § 64.1200(c)(1)
- Records opt-in with a timestamp and the number
- CTIA asks senders to keep the date, time, number and the words used to secure consent.CTIA Messaging Principles and Best Practices (May 2023), 5.1.2
- Toll-free verification submitted by API
- US carriers require a toll-free number to be verified before it sends business texts; an API submits verification from code, one number or many at once.
- Opt-out list readable by API
- A revocation must be honoured within 10 business days; reading the provider's block list keeps your CRM, your other senders and any next provider in step.47 CFR § 64.1200(a)(10)
- Message logs exportable in bulk
- Delivery records prove what was sent and when; a bulk export keeps them after the provider's own window closes.
Who does what: the API or your code
An SMS API is a pipe with a few guards on it. The guards differ by vendor, and the jobs no vendor takes still land on the app. Across the seven, this is how the work splits.
The keyword list matters less than it looks: the FCC rule counts any reasonable way of saying stop, and must be honoured within 10 business days. The words carriers expect are in SMS opt-out keywords; which number type to register is in 10DLC vs toll-free.
| Job | What the APIs here do | What your code still owns |
|---|---|---|
| STOP and opt-out keywords | Twilio, Telnyx, Plivo and AWS block on STOP by default; Vonage once Opt-Out Assist is switched on; Sinch once consent management is on. Bandwidth does nothing on long codes. | Read free-text replies the keyword filter misses, and push every block into your CRM and any other sender. |
| HELP reply | A default or configurable auto-reply on Twilio, Telnyx, Plivo, Vonage and AWS. Bandwidth's docs do not say it answers HELP. | Write the reply: brand name, a contact route and how to stop. |
| Opt-out list | Readable by API on Telnyx, Sinch and AWS. Twilio's Advanced Opt-Out list cannot be read or changed by API. | Keep your own suppression list as the master and check it before every send. |
| 10DLC brand and campaign | All seven take the registration, in a console or by API. | Supply true business details, sample messages and a description of the opt-in flow. |
| Toll-free verification | All seven document a verification request by API. | Show the opt-in: where the number is collected and the words the person agrees to. |
| Consent records | Twilio's Consent Management API holds a status, date and source per number. Plivo and Bandwidth say it is yours. | Save the form, the exact wording shown, the timestamp, IP address and number. |
| Quiet hours | Twilio's Compliance Toolkit holds non-essential texts outside federal and state windows. Telnyx schedules on UTC only. | Work out the recipient's local time and hold marketing sends outside the window. |
| Message logs | Six of the seven document an export or event stream, but some windows are short: Twilio's files last seven days, Telnyx's retrieve endpoint reaches back 10 days, and Bandwidth keeps no message text. | Archive sends, replies and opt-outs in your own store. |
Quiet hours are more than one window
The federal rule bars telephone solicitations before 8 a.m. or after 9 p.m. at the recipient's location. Twilio's toolkit documentation lists eleven states it holds to a stricter window:
- AL
- CT
- FL
- LA
- MD
- MS
- NV
- OK
- TN
- TX
- WA
Twilio Docs, Compliance Toolkit, read 2026-10-22. Texas, for one, runs to noon on Sundays in that list.
A vendor's state list is a convenience, not a ruling. If your provider does not enforce quiet hours, the send-time check lives in your code: test a number against the window with the quiet hours checker, and read the state rules in mini-TCPA state laws.
Vendor by vendor
Each card repeats the table's rows with the detail from the vendor's own docs. Leaving Twilio rather than choosing a first API? Twilio alternatives reads CPaaS providers for a move, including what happens to an existing registration.
Twilio
What it is
A programmable messaging and voice platform. Messaging Services bundle senders and opt-out settings; an optional Compliance Toolkit screens US outbound SMS for consent, reassigned numbers and quiet hours before it sends.
Who it fits
Teams that want the provider to hold back a marketing text at night or to an opted-out or reassigned number, not only to pass the text along.
- Honours STOP and plain-language revocation automaticallyNo
STOP, UNSUBSCRIBE, END, QUIT, STOPALL, REVOKE, OPTOUT and CANCEL are handled by default on long codes. Only single-word replies trigger the block: Twilio says "STOP PLEASE" does not.
- HELP auto-replyYes
HELP is reserved and cannot be removed; Advanced Opt-Out edits the reply and adds keywords per language.
- 10DLC brand and campaign registration in-productYes
Direct brands and campaigns register in the Console onboarding flow; the BrandRegistrations API serves software vendors registering their customers.
- Quiet-hours window by the recipient's time zoneYes
With Compliance Toolkit on, non-essential texts are rescheduled (or blocked) outside federal and state quiet hours by the recipient's area code or ZIP code. US English SMS only.
- Records opt-in with a timestamp and the numberYes
The Consent Management API stores opt-in and opt-out status with the date and source of consent; access comes with Compliance Toolkit or on request.
- Toll-free verification submitted by APIYes
A REST API onboarding flow for toll-free verification, after a Trust Hub business profile.
- Opt-out list readable by APINo
Advanced Opt-Out cannot report or change blocked numbers through the Console or the REST API; the Consent Management API can write statuses in bulk.
- Message logs exportable in bulkYes
Bulk Export delivers daily files of the previous day's messages; files stay downloadable for seven days. US1 region only.
Telnyx
What it is
A messaging, voice and numbers platform. Opt-out rules live on the messaging profile, so a STOP to one number blocks the sender across every number on that profile.
Who it fits
Developers who want natural-language opt-outs caught and the opt-out list readable from code.
- Honours STOP and plain-language revocation automaticallyYes
Keywords are handled by default; AI opt-out detection, a profile setting, treats a high-confidence reply like "please stop texting me" as a STOP.
- HELP auto-replyYes
HELP gets an auto-response; the text, extra keywords and per-country replies are set through the API.
- 10DLC brand and campaign registration in-productYes
Brand, vetting, campaign and number assignment in the Portal or by API.
- Quiet-hours window by the recipient's time zoneNo
Scheduled messages go out at the UTC time you set, not the recipient's local time; the time-zone logic is yours.
- Records opt-in with a timestamp and the numberCheck with the vendor
- Toll-free verification submitted by APIYes
Verification requests by API; Telnyx says review typically takes 1-2 weeks.
- Opt-out list readable by APIYes
A paginated list of opt-out blocks, with filters and optional number redaction.
- Message logs exportable in bulkYes
The retrieve endpoint covers the last 10 days; older records come from an MDR report in the Portal.
Plivo
What it is
A messaging and voice API. A DND service is on by default for US and Canadian long codes and toll-free numbers, and blocks a number after a standard opt-out keyword.
Who it fits
Teams that want keyword opt-outs and HELP replies handled out of the box and will read free-text replies themselves.
- Honours STOP and plain-language revocation automaticallyNo
STOP, END, QUIT, CANCEL, UNSUBSCRIBE, UNSUB and STOP ALL are honoured; Plivo lists "Hey, can you stop texting me?" as an invalid opt-out.
- HELP auto-replyYes
Automatic reply to HELP or INFO on long codes and toll-free numbers.
- 10DLC brand and campaign registration in-productYes
Brand, campaign and number-linking endpoints in the API.
- Quiet-hours window by the recipient's time zoneCheck with the vendor
- Records opt-in with a timestamp and the numberNo
Plivo tells senders to collect consent themselves and to be able to show the opt-in timestamp and number on audit.
- Toll-free verification submitted by APIYes
A TollfreeVerification endpoint in the API.
- Opt-out list readable by APICheck with the vendor
- Message logs exportable in bulkYes
List message records with filters through the API.
Vonage
vonage.com/communications-apis
What it is
The Vonage communications APIs: SMS and the Messages API, plus 10DLC and toll-free registration APIs. Opt-Out Assist manages STOP, HELP and block lists once it is switched on.
Who it fits
Teams that want keywords and reply texts set during campaign registration, and usage records pulled as CSV.
- Honours STOP and plain-language revocation automaticallyCheck with the vendor
Opt-Out Assist blocks after STOP on 10DLC once Vonage support enables it for the brand; free-text replies are not covered in the docs.
- HELP auto-replyYes
Custom Opt-in, Opt-out and Help keywords and reply text, in the dashboard or the 10DLC API.
- 10DLC brand and campaign registration in-productYes
Brand registration, vetting, campaigns and number linking by API.
- Quiet-hours window by the recipient's time zoneCheck with the vendor
- Records opt-in with a timestamp and the numberCheck with the vendor
- Toll-free verification submitted by APIYes
The TFN Registration API manages toll-free registrations in code.
- Opt-out list readable by APICheck with the vendor
- Message logs exportable in bulkYes
The Reports API returns message records as CSV or JSON, in small or large batches.
Bandwidth
What it is
A messaging and voice API with 10DLC campaign and toll-free verification APIs. Opt-in and opt-out keywords on long codes are left to the customer; toll-free STOP is enforced at the network layer.
Who it fits
Teams that already run their own keyword handling and consent store and want registration through the API.
- Honours STOP and plain-language revocation automaticallyNo
No opt-in or opt-out support on long codes or short codes; honouring STOP and keeping lists is the customer's job.
- HELP auto-replyCheck with the vendor
Bandwidth's keyword article covers opt-in and opt-out only, and its toll-free network layer lists no HELP keyword.
- 10DLC brand and campaign registration in-productYes
Campaigns, opt-in, opt-out and HELP keywords and messages are submitted through the API.
- Quiet-hours window by the recipient's time zoneCheck with the vendor
- Records opt-in with a timestamp and the numberNo
Maintaining opt-in and opt-out lists lies with the customer.
- Toll-free verification submitted by APIYes
The band CLI submits a verification request with every carrier field; the verification API covers status and updates.
- Opt-out list readable by APINo
Bandwidth keeps no opt-out list for long codes.
- Message logs exportable in bulkYes
Message history can be queried, but only metadata: Bandwidth does not store message text.
Sinch
What it is
A messaging platform whose Conversation API carries SMS alongside other channels. Its consent management keeps opt-out lists by type (all, marketing, notification) and sends opt-in and opt-out auto-replies.
Who it fits
Teams on the Conversation API that want marketing and notification opt-outs kept apart.
- Honours STOP and plain-language revocation automaticallyNo
Keywords must be an exact match: "stop now please" does not trigger it. The blocklist refreshes every 10 minutes.
- HELP auto-replyCheck with the vendor
- 10DLC brand and campaign registration in-productYes
A 10DLC Brand and Campaign Registration API.
- Quiet-hours window by the recipient's time zoneCheck with the vendor
- Records opt-in with a timestamp and the numberCheck with the vendor
- Toll-free verification submitted by APIYes
The Registration API creates, lists and reads toll-free number verifications.
- Opt-out list readable by APIYes
Public API endpoints for querying the consent lists.
- Message logs exportable in bulkCheck with the vendor
AWS End User Messaging SMS
aws.amazon.com/end-user-messaging
What it is
Amazon's SMS and voice messaging service. Opt-out lists are attached to phone numbers, filled automatically on STOP unless you switch to self-managed opt-outs, and registrations are API resources.
Who it fits
Teams already building on AWS that want opt-outs and delivery events in their own account.
- Honours STOP and plain-language revocation automaticallyCheck with the vendor
CANCEL, END, OPTOUT, QUIT, STOP and UNSUBSCRIBE are handled by default; free-text replies are not covered in the docs.
- HELP auto-replyYes
Long codes come with default HELP and STOP keywords and responses, editable per number or pool.
- 10DLC brand and campaign registration in-productYes
10DLC brand, vetting and campaign registration forms in the console.
- Quiet-hours window by the recipient's time zoneCheck with the vendor
- Records opt-in with a timestamp and the numberCheck with the vendor
- Toll-free verification submitted by APIYes
CreateRegistration creates a registration by type; the console lists a US toll-free registration form.
- Opt-out list readable by APIYes
DescribeOptedOutNumbers reads the list; PutOptedOutNumber adds to it.
- Message logs exportable in bulkYes
Events stream to CloudWatch, Amazon Data Firehose or an SNS topic you own.
How we read the claims
Questions developers ask
Does an SMS API make our texting TCPA-compliant?
No. The provider moves the message and, depending on the vendor, blocks numbers that replied STOP. Whether you had consent to send it is still your question, and the statutory damages are $500 per call or text, up to three times that ($1,500) if the court finds the violation willful or knowing.
If the provider handles STOP, do we still need to read replies?
Yes. The FCC rule (47 CFR § 64.1200(a)(10)) lets a person revoke consent "by using any reasonable method": seven reply words count on their own, and other words count if a reasonable person would read them as a request to stop. It must be honoured within ten business days. Most providers match keywords only; Plivo's own docs list "Hey, can you stop texting me?" as a reply its keyword filter does not catch. Route every inbound reply your filter misses to a person or a classifier.
What consent records should our app keep?
CTIA's guidelines list the timestamp, the consent medium, the words or experience shown, the campaign, the IP address, the phone number and the identity of the person. Plivo and Bandwidth say in their docs that collecting and keeping consent is the customer's job; Twilio's Consent Management API can hold a status, date and source per number, but the opt-in screen and its wording are still yours to save.
10DLC or toll-free: which should a small business text from?
Both need paperwork before carriers accept the traffic. 10DLC means a registered brand and campaign with The Campaign Registry; a toll-free number needs toll-free verification. Every API on this page can do 10DLC registration, and six of the seven document toll-free verification through an API. On US toll-free numbers, STOP is enforced at the network layer whatever the provider does, which Bandwidth and Vonage both note.
How long should we keep message logs?
Longer than most providers keep them for you. Bandwidth stores message metadata only, never the text; Telnyx's retrieve endpoint reaches back 10 days; Twilio's Bulk Export files stay downloadable for seven days after they are made. A do-not-call request must be honoured for 5 years, so archive sends, replies and opt-outs in your own store for at least that long.
Sources
- 47 CFR § 64.1200(a)(10)fetched 2026-10-22
- CTIA Messaging Principles and Best Practices (May 2023), 5.1.2.1fetched 2026-10-22
- 47 U.S.C. § 227(b)(3) (private right of action)fetched 2026-10-22
- Twilio Docs: Programmable Messaging and A2P 10DLCfetched 2026-10-22
- Vonage Docs: Enabling Opt-Out Assistfetched 2026-10-22
- Twilio help centre: Twilio support for opt-out keywords (SMS STOP filtering)fetched 2026-10-22
- Twilio Docs: Advanced Opt-Outfetched 2026-10-22
- Twilio Docs: A2P 10DLC BrandRegistrations resourcefetched 2026-10-22
- Twilio Docs: Compliance Toolkitfetched 2026-10-22
- Twilio Docs: Consent Management APIfetched 2026-10-22
- Twilio Docs: Toll-free verification using the APIfetched 2026-10-22
- Twilio Docs: Bulk Export APIfetched 2026-10-22
- Telnyx Docs: Opt-In/Out Managementfetched 2026-10-22
- Telnyx Docs: 10DLC quickstartfetched 2026-10-22
- Telnyx Docs: Schedule SMS and MMS messagesfetched 2026-10-22
- Telnyx Docs: Toll-free verificationfetched 2026-10-22
- Telnyx API: List opt-outsfetched 2026-10-22
- Plivo Docs: DND Servicefetched 2026-10-22
- Plivo Docs: 10DLC Brand APIfetched 2026-10-22
- Plivo Docs: US messaging best practicesfetched 2026-10-22
- Plivo Docs: Toll-free verification APIfetched 2026-10-22
- Plivo Docs: Messages APIfetched 2026-10-22
- Vonage Docs: Opt-Out Assist keyword set-upfetched 2026-10-22
- Vonage Docs: 10DLC API overviewfetched 2026-10-22
- Vonage Docs: TFN Registration overviewfetched 2026-10-22
- Vonage Docs: Reports API overviewfetched 2026-10-22
- Bandwidth: Does Bandwidth handle opt-in and opt-out keywords?fetched 2026-10-22
- Bandwidth Docs: CSP Campaign APIfetched 2026-10-22
- Bandwidth Docs: band tfv submitfetched 2026-10-22
- Bandwidth Docs: Messaging (message storage)fetched 2026-10-22
- Sinch Docs: Consent management (Conversation API)fetched 2026-10-22
- Sinch Docs: 10DLC Brand and Campaign Registration APIfetched 2026-10-22
- Sinch: TFN Verification APIfetched 2026-10-22
- AWS: Keywords in AWS End User Messaging SMSfetched 2026-10-22
- AWS: Origination identity registrationfetched 2026-10-22
- AWS API: CreateRegistrationfetched 2026-10-22
- AWS API: DescribeOptedOutNumbersfetched 2026-10-22
- AWS: Event destinationsfetched 2026-10-22