Health data infrastructure · Provider directories
Ribbon Health
An API built to answer a question the American health system keeps getting wrong: is this doctor real, in network, and reachable at the number listed. Founded in 2016 as HealthWiz, sold to H1 in December 2024.
Fifty phone numbers for one doctor
Ask a health plan where one of its contracted cardiologists actually sits, and no single system can answer. The plan has a roster. The hospital has a directory page. The state has a license file. A claims feed has a billing address. None agree.
“We see over 50 phone numbers per doctor,” Nate Maslak told HealthLeaders Media in 2021. “And that’s just phone numbers.” Ribbon Health was built on the idea that this is a probability problem rather than a filing problem: aggregate every source, then score the answer.
“If 800 sources say that Dr. Smith is at 123 Main Street, and 200 sources say she’s at 400 University, what’s the probability that either or both of those locations are right at this moment in time?” Maslak said in the same interview. “Our algorithms assign a confidence score to that, and that’s what we deliver to our customers.”
What the auditors found
The scale of the problem is not a vendor talking point. It sits in federal audit reports. In its second round of Medicare Advantage directory reviews, CMS checked 6,841 providers at 14,869 locations across 64 plans and found 52.20 percent of locations carried at least one inaccuracy: wrong place, wrong phone number, or a listing that said the provider was taking new patients when the provider was not. Round three, a year later, found 48.74 percent of 10,504 locations inaccurate, with plan level rates from 4.63 to 93.02 percent.
In May 2023 Senate Finance Committee staff made 120 calls to mental health listings across 12 plans in six states. A third were wrong numbers, dead ends or unreturned calls. Appointments could be booked 18 percent of the time. In Oregon, staff booked none.
Two founders, two illnesses
Maslak immigrated from Russia to Cleveland as a child with his mother. When she developed severe joint pain he was a healthcare consultant with provider relationships, living in a city full of famous hospitals, and he still could not route her correctly. She saw a back pain specialist, then a string of others, and ran up medical debt that Forbes reported almost pushed her into bankruptcy. Nate Fox had the opposite experience: born with a severe hearing impairment, he was routed to the right specialists early.
They met in 2015, at Harvard Business School according to Contrary Research, and built a care navigation product for employers. Then the complaints arrived: wrong addresses, wrong numbers, providers who no longer took the insurance or no longer practiced. The data they had licensed turned out to be less than 50 percent accurate.
The pivot the filings show
The SEC record tracks the turn precisely. The first two Form D notices, filed in 2017 and 2018, come from HealthWiz, Inc., a Delaware corporation formed in 2016 at 125 Western Avenue in Boston. They are small: $110,000 sold of $1,500,000 offered to three investors, then $90,000 of $1,050,000 to three investors. By February 2020 the same identifier, CIK 0001716554, files as Ribbon Health, Inc. at 188 Grand Street in New York, reporting $11,819,986 sold to 32 investors, with Julie Yoo of Andreessen Horowitz listed as a director. The company had stopped selling navigation and started selling the data layer underneath it.
The law catches up, then the company sells
Regulation kept moving Ribbon’s way. The No Surprises Act, codified at 42 U.S.C. 300gg-115, requires plans from 2022 to verify directory information at least every 90 days, answer a member’s phone question about network status in writing within one business day, and update the database within two business days of hearing from a provider. CMS separately required Medicare Advantage, Medicaid and CHIP plans to publish directory data through a standards based API by January 1, 2021. Then section 6220 of the Consolidated Appropriations Act, 2026 enacted the REAL Health Providers Act: from plan year 2028, Medicare Advantage plans must verify every 90 days, flag unverified listings, drop out of network providers within five business days and report an accuracy score to CMS, published from 2029.
Ribbon did not stay independent for it. H1 signed a definitive agreement on December 12, 2024 and announced it on January 8, 2025, paying cash and stock in an amount it did not disclose. H1 chief executive Ariel Katz told Fierce Healthcare that Ribbon had more than 50 customers, revenue in the tens of millions, and 20 million to 25 million Americans a year finding a provider through it. The platform now sells as H1 for Health Plans and Digital Health, and as of September 2025 the documented endpoints still resolve to api.ribbonhealth.com.
What is proven, and what is still claimed
| Evidence | What the record shows | Source type |
|---|---|---|
| SEC Form D filings | Four notices, CIK 0001716554, all Rule 506(b): 2017 ($110,000 sold, as HealthWiz); 2018 ($90,000); 2020 ($11,819,986, 32 investors); 2021 ($3,500,000, 2 investors). Total on the SEC record: $15,519,986. | Public record |
| CMS directory audits | Round 2: 52.20% of 14,869 Medicare Advantage directory locations inaccurate. Round 3: 48.74% of 10,504 locations, plan range 4.63% to 93.02%. | Public record |
| Senate secret shopper study | May 3, 2023. 120 calls, 12 plans, 6 states. 33% inaccurate, non working or unreturned. Appointments obtained 18% of the time. | Public record |
| Federal directory mandates | 42 U.S.C. 300gg-115 from 2022. CMS Provider Directory API required by Jan 1, 2021. REAL Health Providers Act effective plan year 2028, scores published from 2029. | Public record |
| Named customers | Oak Street Health and Well (2020); PacificSource, Health Advocate, Decent, Firefly Health (2021); Healthee and two unnamed top five national plans (2024); Transcarent and Rightway (2025). | Company and press stated |
| Product performance claims | 99.9% coverage of US providers and facilities, intake costs down up to 95%, accuracy improved up to 90%, tickets down 24%. All from the March 2024 release. No independent audit found. | Company-stated |
| Scale at acquisition | More than 50 customers, tens of millions in revenue, 20 to 25 million users a year, per Ariel Katz. | Acquirer-stated |
| Total capital raised | $55 million per the company in Nov 2021; $53.8M per AlleyWatch and Contrary; $75 million per Katz in 2025. The SEC record shows $15.5M. | Accounts differ |
| Regulatory, clinical and IP record | No FDA record, trials, NIH or NSF awards or PubMed papers. No federal prime contracts in USAspending. No granted US patents or SOC 2 or HITRUST attestation surfaced. | Not found |
Read plainly: the problem Ribbon sold against is documented by federal auditors and the Senate, in hard numbers, over a decade. Ribbon’s performance against it is documented by Ribbon. Between them sits an acquisition paid in cash and stock, and figures the acquirer put its own name on. That is more than most private data companies disclose, and less than an audit.
What to watch
- The first REAL Health Providers Act accuracy scores, analysed for plan year 2028 and published from 2029, the first time directory accuracy becomes a comparable number.
- Whether H1 keeps the Ribbon API as a standalone product. The endpoints still carry the ribbonhealth.com domain.
- Any independent measurement of accuracy. Every figure in circulation comes from the vendor.
- CMS and ONC implementation of the REAL Act, including what counts as verification and what a member is owed after relying on a wrong listing.
In their words
“If 800 sources say that Dr. Smith is at 123 Main Street, and 200 sources say she’s at 400 University, what’s the probability that either or both of those locations are right at this moment in time?”
Nate Maslak, CEO, HealthLeaders Media, 2021 · Independent
“Ribbon collects data from over a thousand different data sources at any given time, and then we try to figure out what’s right and what’s wrong.”
Nate Maslak, Forbes, November 2021 · Independent
“when insurance companies host ghost networks, they are selling health coverage under false pretenses, because the mental health providers advertised in their plan directories aren’t picking up the phone or taking new patients.”
Senator Ron Wyden, chair, Senate Finance Committee, May 3, 2023 · Public record
“One of the reasons that Ribbon stood out to us was its ability to create network effects. Every single day, every single minute that organizations use Ribbon, the data gets better and better.”
Julie Yoo, general partner, Andreessen Horowitz, Forbes, 2021 · Investor
“Our mission is to connect the world to the right doctor. They were doing it for patients. We were doing it for pharma.”
Ariel Katz, CEO, H1, to Fierce Healthcare, January 2025 · Independent
“From the moment Ariel and I first met, it was clear that Ribbon and H1 were destined to collaborate.”
Nate Maslak, acquisition release, January 8, 2025 · Company release
Related companies
Sources
- Public recordForm D filings, CIK 0001716554, HealthWiz and Ribbon Health
- Public recordOnline Provider Directory Review Report, Round 2
- Public recordOnline Provider Directory Review Report, Round 3
- Public recordGhost networks secret shopper study
- Public record42 U.S.C. 300gg-115 and CMS interoperability rules on directory APIs
- IndependentA more accurate Medicare Advantage provider directory on the way
- IndependentWhy General Catalyst, a16z and Rock Health are backing Ribbon Health
- IndependentAI and APIs team up to solve provider directory problem for patients
- IndependentH1 acquires Ribbon Health
- IndependentHealthcare analytics platform H1 has acquired Ribbon
- IndependentRibbon Health business breakdown
- CompanyRibbon Health raises $10.25 million
- CompanyRibbon Health raises $43.5M Series B, and the Mar 2024 Provider Data Platform launch
- CompanyH1 acquires Ribbon Health and unveils 2025 roadmap
Profile researched and written by Healthcare Discovery. Last updated September 29, 2026.
