Your website and mobile app are only the front window. Behind them sits an API (application programming interface), the set of connections that actually reads and changes customer data on your servers. Attackers know this and skip the front window entirely, sending requests straight to the API. That’s why larger clients now ask for an API pentest (an authorized attack by hired security testers) on the vendor questionnaire, and why auditors want to know whether last year’s test reached it.
Plenty of firms put “API testing” on their service list. Far fewer focus on the API itself, logging in as every type of user and testing the endpoints your screens never call. This guide compares five US-based companies that put real focus on API penetration testing. If you’re new to the topic, CYBRI’s API penetration testing guide covers the basics first.
The five companies on this list:
- CYBRI: best for SaaS companies that want hands-on testing under every user role, with a report ready for an auditor or an enterprise customer
- NetSPI: best for large companies with big API catalogs that want enterprise-scale testing from in-house staff
- Raxis: best for companies running many kinds of APIs (GraphQL, gRPC, webhooks) that want ongoing testing alongside a yearly test
- Cobalt: best for teams that need an API test booked and started within days through a self-service platform
- Synack: best for companies with headless APIs that want a large pool of vetted researchers and proof of what was tested on each endpoint
Why APIs Need a Specialized Pentest Partner
An API test sounds like a smaller version of a web app test. In practice it’s closer to the opposite. The website only shows a customer what their screens allow, while the API underneath will answer any request that reaches it. The four points below explain why the vendor you choose matters.
Most API Breaches Start With a Normal Login
The person who breaks into an API usually holds an ordinary customer account. They sign in, look at the requests their own account sends, and change one detail, such as an order number, to see what comes back. If the API returns someone else’s order, the breach is already done. This kind of flaw (called BOLA, or broken object level authorization) sits at number one on the OWASP API Security Top 10, the industry’s ranked list of API risks, and CYBRI’s guide to what an API pentest should check against the OWASP API Top 10 walks through the rest of the list. The article on IDOR, BOLA, and privilege escalation goes deeper on why these permission mistakes are so common.
Scanners Can’t Tell Whose Data Is Whose
An automated scanner reads the response and checks for known technical patterns. It has no idea that a dispatcher shouldn’t see payroll records, or that customer A’s invoice should never load for customer B. Both responses look perfectly healthy to a tool. Finding these flaws takes a tester who understands your business and checks, endpoint by endpoint, what each role is supposed to reach. An API with 60 endpoints and 4 user roles adds up to 240 of those decisions.
The APIs Nobody Is Watching
Old API versions tend to stay online long after the team moves on, because older copies of the mobile app still call them. Staging copies end up reachable from the internet. Partner integrations get their own endpoints that never appear in the main documentation. A good tester maps all of this before attacking anything, since a test can only cover the APIs someone knows about. For apps on phones, a mobile application pentest often turns up endpoint addresses and keys stored inside the app itself.
Auditors and Enterprise Buyers Want Proof
SOC 2, PCI DSS, HIPAA, and ISO 27001 don’t name the API specifically. They expect a credible test of every system that handles customer or regulated data, and for most modern products the API is that system. PCI DSS is the most direct: requirement 11.4 calls for testing the application layer at least once a year and after significant changes. A report that tags each finding with its OWASP API Top 10 entry and the control it supports saves your compliance lead a week of matching things up by hand.
1. CYBRI
Best for: SaaS companies that want hands-on testing under every user role, with a report ready for an auditor or an enterprise customer
CYBRI is a New York penetration testing company that has worked mainly with SaaS, fintech, and healthcare companies since 2017. A senior US-based, OSCP-certified tester leads each engagement and works manual-first, with automated tools used to cover ground faster rather than to replace the person. API tests usually run gray box. The client hands over its API documentation (a Postman collection or an OpenAPI/Swagger file is enough) and a test account for each user role, and testers call the endpoints directly as each one of those users.
The first step is mapping. Testers list every endpoint they can find, including old versions and anything the documentation left out, before working through the OWASP API Top 10 against the client’s own business rules. Most of the time goes into permissions: can a regular user reach admin functions, can one customer pull another’s records, does a paid tier hold up when someone tries to take more than they pay for. Critical findings get reported the same day, ahead of the final report.
The report has two parts. Leadership and auditors get a plain-language summary, while engineers get technical findings rated on CVSS 4.0 (the standard severity scale) with steps to fix each one. Findings are mapped to SOC 2, PCI DSS, HIPAA, or ISO 27001 as needed. A debrief call with the testers follows delivery, and retesting of fixes within 90 days is included, so the client ends up with proof that the fixes hold. Pricing is fixed before work starts. More detail is on the API penetration testing service page.
2. NetSPI
Best for: large companies with big API catalogs that want enterprise-scale testing from in-house staff
NetSPI has worked in penetration testing since 2001 and is based in Minneapolis. Its in-house team of more than 350 security specialists gives it the capacity to take on large API portfolios. APIs get dedicated attention inside its penetration testing as a service (PTaaS) platform, with a stated commitment to full OWASP API Top 10 coverage plus manual business logic testing.
Engagements run in three phases: information gathering, testing and evaluation, and analysis and reporting. Beyond the OWASP API Top 10, testers look at business logic flaws and unrestricted resource consumption, such as endpoints with weak or missing rate limits. Each finding gets a CVSS 3.1 severity score and is mapped to its OWASP category. Clients are notified of vulnerabilities as they’re found rather than waiting for the final report, and results can be compared across multiple assessments, which suits security teams handling dozens of applications at once.
3. Raxis
Best for: companies running many kinds of APIs (GraphQL, gRPC, webhooks) that want ongoing testing alongside a yearly test
Raxis is an Atlanta penetration testing firm that has done manual testing since 2011. Its senior engineers are US-based, and the engineer who scopes the project is the same one who runs the test and later checks the fixes. APIs are a clear focus, and the firm is direct about where the effort goes: authorization is the main event, so most of the hours go into testing every role (no login, standard user, admin) and every boundary between customer accounts.
Coverage is wide. Raxis tests REST, GraphQL, SOAP, and gRPC (a fast format common between internal services), plus WebSockets, webhooks, mobile app backends, partner APIs, and serverless functions. Testing follows the 2023 OWASP API Security Top 10 and works with or without documentation, so forgotten and undocumented endpoints are in scope. Each finding comes with the exact request that triggered it, proof of impact, and a fix written for the client’s tech stack, and the retest costs nothing extra. Clients choose between a fixed-window test before a launch or audit and a continuous subscription with live findings that sync to Jira or GitHub. The page lists PCI DSS, SOC 2, HIPAA, and ISO 27001 among the requirements its API work supports.
4. Cobalt
Best for: teams that need an API test booked and started within days through a self-service platform
Cobalt is a San Francisco company, founded in 2013, that describes itself as a pioneer of PTaaS, the model where customers book and track pentests through an online platform. Its tests are run by Cobalt Core, a vetted community of more than 500 pentesters whose members average 11 years of experience.
The API service covers REST, GraphQL, and SOAP APIs, along with API gateways and the microservices behind them, and its methodology draws on the OWASP API Security Top 10 and OWASP’s ASVS checklist. Cobalt describes the work in four steps: map the attack surface, model access and business logic, run enumeration and scanning, and exploit manually. Findings appear in the platform in real time, and retesting is unlimited within a seven-day turnaround. Pricing runs on a flexible credit model that scales with the amount of testing a team needs.
5. Synack
Best for: companies with headless APIs that want a large pool of vetted researchers and proof of what was tested on each endpoint
Synack is based in Redwood City, California, and has served customers since 2013. Its testing comes from the Synack Red Team, a community of more than 1,500 security researchers around the world who pass a five-step vetting process that includes a skills test, a background and identity check, and an interview. In late 2022 the company added API pentesting aimed at “headless” APIs, meaning APIs sold or used on their own with no website or app in front of them. The focus there is the endpoints a web app test never reaches, including ones with no screen behind them at all.
Customers upload their API documentation as a Postman collection or OpenAPI file, and the platform turns each endpoint into a separate task. Only researchers with proven API testing skills get activated on that work, and Synack’s internal operations team reviews every submission before the customer sees it, which cuts down on false alarms. The deliverable that stands out is the proof-of-coverage report, which shows what was attempted against each endpoint, screenshots included.
How to Choose the Right API Pentest Partner
API testing providers differ in who does the work, how deep they go into permissions, and what you’re left holding at the end. Use these points to compare the shortlist side by side:
| Criteria | What to look for |
| Who does the testing | A firm’s own testers or a vetted community of researchers. Ask who confirms each finding before it reaches you, and whether you can talk to that person during the test. |
| User roles in scope | A quote that lists every role (customer, manager, admin, partner) and explains how testers will try to cross between them, including from one customer account into another. |
| Endpoint discovery | A plan for finding old API versions, undocumented endpoints, and anything only the mobile app calls, not just what’s in your Postman collection. |
| API types covered | REST, GraphQL, SOAP, gRPC, webhooks, or whatever your stack actually runs. |
| Testing approach | Gray box as the usual starting point: API documentation plus a test account for each role. Manual work on permissions and business logic, with tools used for coverage. |
| Retesting | Whether retests are included, how long the window stays open, and whether the report gets updated once fixes are confirmed. |
| Reporting quality | An executive summary, CVSS severity scores, the exact request that triggers each issue, and labels tying findings to the OWASP API Top 10 and to SOC 2, PCI DSS, HIPAA, or ISO 27001. |
| Engagement model | A single test before an audit or launch, several tests a year, or a continuous subscription. The right one follows how often your API changes. |
Size matters too. A SaaS company with one API and a SOC 2 deadline needs clear guidance and a report the auditor accepts without edits. A company with hundreds of endpoints across several products will care more about capacity, scheduling, and how findings flow into its ticketing system.
Final Thoughts
Each company on this list takes API testing seriously, and the best pick comes down to the size of your API and how you prefer to buy testing. For a SaaS company that wants senior US-based testers working through every user role by hand, a report ready for an auditor or an enterprise customer, and a price agreed before work starts, CYBRI is a strong fit. Testers stay reachable throughout the engagement, and fixes get retested within 90 days. A short scoping call is enough to size the work, so contact CYBRI to talk through your API and your deadlines.
Frequently Asked Questions
Does my web app pentest already cover the API?
Only partly. A web app test reaches the API through the requests your screens send. An API test calls every endpoint directly, including admin functions, old versions, and endpoints used only by the mobile app or a partner. If your product is mostly an API, or your mobile app shares the same backend, a test focused on the API is worth scoping.
How often should an API be tested?
The common recommendation is at least once a year, plus after changes that touch access: a new API version, a new user role, a new partner integration, or a change to how logins work. Teams that ship API changes every few weeks usually move to several tests a year so each release gets checked.
What do testers need before an API test starts?
API documentation (a Postman collection or OpenAPI/Swagger file), a test account or API key for each user role, the address of the environment to test, and any firewall allowlisting. Having all of it ready at kickoff is the simplest way to keep the timeline short.
Ready to Test Your API?
CYBRI runs manual-first API penetration tests with every user role in scope. Senior OSCP-certified testers flag critical issues the same day, findings appear in the BlueBox dashboard, and every fix is retested within 90 days with an updated report. Get a quote to scope a test for your API.
