Glossary
What is STIR/SHAKEN?
STIR/SHAKEN is the caller ID authentication framework US voice carriers use to digitally sign outbound calls and verify the signature on the receiving side. Each call carries an attestation level, A, B or C, that says how strongly the originating carrier vouches for the caller's right to use the number. The FCC has required it since 2021 under the TRACED Act.
Key STIR/SHAKEN terms
| STIR | Secure Telephone Identity Revisited. A set of IETF standards (including RFC 8224 and RFC 8225) for attaching a cryptographic signature to a call's caller ID in SIP signaling. |
| SHAKEN | Signature-based Handling of Asserted information using toKENs. The ATIS/SIP Forum framework that defines how carriers deploy STIR in their networks, including the attestation levels and the certificate governance. |
| Attestation | The originating carrier's statement about how well it knows the caller and the number. Three levels: A (full), B (partial) and C (gateway). |
| A attestation | Full. The carrier knows the customer and has confirmed the customer is authorized to use the calling number. This is the level that lets a receiving carrier display a "verified" indicator. |
| B attestation | Partial. The carrier knows the customer but has not verified that the customer is authorized to use the calling number, which is common when a business brings its own numbers to a new provider. |
| C attestation | Gateway. The carrier is passing the call from another network and cannot vouch for the caller or the number, for example international traffic entering the US. |
| TRACED Act | The Pallone-Thune TRACED Act of 2019, the federal law that directed the FCC to require voice service providers to implement STIR/SHAKEN. |
| Robocall Mitigation Database | An FCC database where voice service providers certify their STIR/SHAKEN implementation or robocall mitigation program. Carriers may not accept traffic from providers that are not listed. |
How STIR/SHAKEN works
When a call leaves the originating carrier, that carrier creates a signed token (a PASSporT, under RFC 8225) containing the calling number, the called number, a timestamp and the attestation level, and attaches it to the call's SIP INVITE in an Identity header. The signature uses a certificate issued under the SHAKEN governance system, so other carriers can check who signed it.
When the call arrives at the terminating carrier, that carrier fetches the signing carrier's certificate, verifies the signature, and passes the result to its call analytics. Depending on the handset and carrier, a fully attested call may show a "Caller Verified" checkmark or label. The verification result is also one of the inputs carriers use when deciding whether to label or block a call. STIR/SHAKEN only works end to end on IP (SIP) networks; calls that cross legacy TDM segments can lose the signature.
Why STIR/SHAKEN matters if your team calls leads
- Attestation affects how your calls display: calls with A attestation are the ones eligible for a verified indicator. B or C attestation does not mean the call is blocked, but it gives analytics less reason to trust it.
- Your provider sets the level, not you: numbers your carrier issued to you, or numbers you have proven you own, usually get A. Numbers brought from elsewhere without a verification step often get B.
- It does not fix spam labels on its own: "Spam Likely" and similar tags come from analytics that weigh volume, answer rates and complaints. Authentication is one input among several.
- It does nothing for the numbers you dial: STIR/SHAKEN is about the calling party. Dead numbers, landlines on an SMS list, and VoIP lines on a cold-call list still have to be found before the campaign, which is what a lookup is for.
- It is not a compliance check: consent, Do Not Call status and calling hours are separate obligations under the TCPA and state law.
STIR/SHAKEN vs. a phone lookup
| STIR/SHAKEN | TrueSearch lookup | |
|---|---|---|
| Who does it? | The originating and terminating voice carriers, in their SIP networks | TrueSearch, on the list you upload before you dial |
| What does it check? | Whether the caller ID on an outbound call is signed and how strongly the originating carrier vouches for it | Whether each number on your list is valid or dead, its line type and its carrier |
| When does it run? | At call time, on every call, between networks | Before the campaign, on the whole file at once |
| Can you see the result? | Indirectly: a "Caller Verified" checkmark or similar label on some receiving phones, or a spam tag if analytics flag the call | Yes: a row per number in your CSV or API response |
| Does it stop dead dials? | No. It authenticates the caller, not the number being called | Yes. Dead and invalid numbers are flagged before anyone dials them |
| Does it check Do Not Call? | No | No. TrueSearch does not scrub DNC or litigator lists |
Official sources
- FCC: Combating Spoofed Robocalls with Caller ID Authentication
- Pallone-Thune TRACED Act (S.151, 116th Congress)
- FCC Robocall Mitigation Database
- RFC 8224: Authenticated Identity Management in SIP
- RFC 8225: PASSporT
This page is a plain-language summary, not legal or engineering advice. Your voice provider controls how your calls are signed.
What TrueSearch returns, and does not
| Valid or dead (disconnected / not assigned) | Yes, every number |
| Line type: mobile, landline, VoIP, toll-free | Yes, every number |
| Carrier name | Yes, every number |
| Bulk upload (CSV or Excel) | Yes, results in about 30 seconds per 1,000 numbers |
| REST API | Yes (JSON, one API key) |
| Claude / ChatGPT / Cursor connector (MCP) | Yes |
| National or state Do Not Call check | No, not yet |
| Known TCPA litigator check | No, not yet |
| FCC Reassigned Numbers Database check | No |
| Starting price | $97/month for 5,000 numbers, 7-day free trial |
| One-off list | $20 per 1,000 numbers, no subscription |
Upload a CSV or Excel file. Every number comes back valid or dead, mobile, landline, VoIP or toll-free, with its carrier, before your dialer places a single signed call.
Starter: $97/month for 5,000 numbers after the 7-day trial. Cancel anytime.
Questions
What does STIR/SHAKEN stand for?
STIR is Secure Telephone Identity Revisited, a set of IETF standards for signing caller ID information. SHAKEN is Signature-based Handling of Asserted information using toKENs, the framework from ATIS and the SIP Forum that defines how carriers deploy STIR in production networks.
What does STIR/SHAKEN actually do?
When a call leaves the originating carrier's network, that carrier attaches a digitally signed token to the call's SIP signaling. The token says which number is calling and how confident the carrier is that the caller is allowed to use it (the attestation level). The terminating carrier checks the signature against the signing carrier's certificate before the call reaches the phone. It is caller ID authentication, not call blocking by itself, though carriers and analytics providers use the result as an input to blocking and labeling.
What are the STIR/SHAKEN attestation levels?
A, B and C. A (full) means the carrier knows the customer and has verified they are authorized to use the number. B (partial) means the carrier knows the customer but has not verified their right to the number. C (gateway) means the carrier is just passing the call along and cannot vouch for the caller.
Is STIR/SHAKEN required?
Yes, for US voice service providers. The TRACED Act of 2019 directed the FCC to mandate it, and the FCC required large providers to implement STIR/SHAKEN in the IP portions of their networks by June 30, 2021, with later deadlines for smaller providers and for intermediate providers. Providers also have to file in the FCC Robocall Mitigation Database, and carriers must refuse traffic from providers that are not in it.
Why do my calls show as "Spam Likely" even with STIR/SHAKEN?
STIR/SHAKEN authenticates who is calling; it does not decide whether a call is wanted. Spam and scam labels come from carrier analytics that look at call volume, answer rates, call duration, complaints and other patterns. A low attestation level (B or C) can make a label more likely, but a full A attestation does not guarantee a clean display. Fixing labels usually means registering your numbers with the carriers' analytics vendors and keeping calling patterns reasonable.
How do I get A-level attestation?
Your voice provider assigns attestation, not you. Providers generally give A attestation to numbers they issued to you or numbers you have proven you own, for example through a letter of authorization or a verification process. Ask your carrier or dialer vendor what they require.
Does STIR/SHAKEN help me verify the numbers on my lead list?
No. It works on the calling party's identity as a call is placed. It says nothing about whether the number you are dialing is in service, whether it is a cell phone or a landline, or who the carrier is. That is what a phone validation or carrier lookup does before the call.
Does TrueSearch do STIR/SHAKEN?
No. TrueSearch does not place or sign calls. It checks the numbers on your list against carrier data and returns valid or dead, line type (mobile, landline, VoIP or toll-free) and carrier. STIR/SHAKEN is handled by your voice provider on the calls themselves.
Related: what is CNAM?, what is a carrier lookup?, what is a VoIP number?, what is the TCPA?, the free carrier lookup and the free cost of dead dials calculator.
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This guide is general information, not legal advice. TrueSearch for Business checks validity, line type and carrier from licensed telecom data. It does not check the National Do Not Call Registry, state DNC lists or the FCC Reassigned Numbers Database. Not a consumer reporting agency; not for FCRA purposes.