The top API penetration testing companies for most buyers in 2026 are White Knight Labs, for manual API testing built into a playbook-driven web application methodology; Blaze Information Security, for the most detailed protocol coverage we found, spanning REST, GraphQL, gRPC and WebSockets; and Cobalt, for fast PTaaS API tests with unlimited retesting inside a seven-day window. This list covers seven more firms, from audit-focused providers to European specialists, with what each one says it tests and delivers.
This list is for engineering, product security and compliance leads who need an outside firm to attack their APIs, whether public, partner-facing or behind a mobile app. We only included service firms with a named API penetration testing offering, or a web application testing page that explicitly scopes APIs. API security products, scanners and gateways are not on this list. We compared each firm on protocol coverage, alignment with the OWASP API Security Top 10, manual testing, deliverables, retests and published pricing, using the companies’ own service pages. For testing of full web applications, see our web application penetration testing companies list, and for a broader view of application security vendors, see our application security companies roundup.
API Penetration Testing Companies At A Glance
Company
Headquarters
Best For
API Testing Coverage
White Knight Labs
Guys Mills, Pennsylvania, USA
Manual testing of APIs alongside web apps
API enumeration, auth, access control, IDOR, SSRF, chained flaws
Blaze Information Security
Not published
Teams running several API styles
REST, GraphQL, gRPC, WebSocket, OWASP API Top 10
Cobalt
Boston, Massachusetts, USA
PTaaS buyers who retest often
REST, SOAP, GraphQL, gateways, microservices
NetSPI
Minneapolis, Minnesota, USA
Large API catalogs and role-heavy apps
OWASP API Top 10, anonymous and authenticated testing, CVSS scoring
Packetlabs
Toronto, Ontario, Canada
APIs that move money, data or privileges
REST, GraphQL, gRPC, SOAP, internal and third-party APIs
Triaxiom Security
Charlotte, North Carolina, USA
Multi-tenant SaaS with a fixed process
Fuzzing, injection, auth bypass, tenant isolation
Schellman
Tampa, Florida, USA
Buyers pairing tests with audits
Proxied manual testing from Swagger or Postman collections
1. White Knight Labs — Manual API Testing Inside A Playbook-Driven Web App Methodology
White Knight Labs is an offensive security firm founded in 2017, with offices in Guys Mills, Pennsylvania, and Grand Rapids, Michigan. Its web application penetration testing service is built for applications and APIs together, on the reasoning that as applications connect through APIs, the attack surface grows quickly. Scoping explicitly identifies which web applications, APIs and components are in scope, and reconnaissance maps the architecture and exposed endpoints, the tech stack and the business logic.
The hands-on work is where APIs get most of their attention. Testers manually enumerate directories, APIs and parameters to uncover hidden or unexposed functionality, review authentication, session management and access controls, and then safely exploit what they find, testing business logic, chaining vulnerabilities and checking for SSRF, IDOR and XXE. Each engineer works from a custom playbook built for the target application, which covers issues that fall outside standard frameworks. The methodology aligns with the OWASP Top 10 and the CWE Top 25, and automated scanners are used early, with manual testing doing most of the work.
Deliverables include an executive summary, detailed findings with proof of concept and risk ratings, business impact for each vulnerability and remediation guidance for developers, with optional remediation testing and an updated report. The firm holds CREST Pathway+ status and is a Service-Disabled Veteran-Owned Small Business.
Best for: Teams that want APIs tested by hand alongside the web applications that use them, with real business logic and authorization abuse.
Blaze Information Security publishes the most protocol-specific API testing scope we found. REST testing covers endpoint enumeration, HTTP method tampering, parameter pollution and rate limits. GraphQL testing covers introspection, query depth and batching abuse and field-level authorization. gRPC testing covers protobuf and reflection analysis, stream handling and metadata, and WebSocket testing covers session handling, message tampering, cross-origin behavior and subscription abuse.
Coverage follows the OWASP API Security Top 10, adapted to each client’s roles and business logic, with researchers focusing on how identities, roles, objects and rules interact rather than relying on scanners. Every finding is validated by hand and delivered with reproducible requests and responses plus remediation guidance. Blaze also references NIST SP 800-115, PTES, OWASP ASVS and the CWE Top 25. When retesting is in scope, researchers replay the original requests and update the report.
Best for: Engineering teams running more than one API style, especially GraphQL or gRPC, that want each tested with its own techniques.
3. Cobalt — PTaaS API Testing With Unlimited Seven-Day Retests
Boston-based Cobalt runs API pentests through its PTaaS platform using testers from the Cobalt Core, its vetted community. The methodology adapts across REST, SOAP, GraphQL, API gateways and microservices, and follows the OWASP API Security Top 10 and OWASP ASVS. Cobalt says human experts handle manual exploitation and business logic testing, while AI helps with reconnaissance, enumeration, scanning and triage.
The retest model is the standout: each finding comes with unlimited retesting within a seven-day SLA, which suits teams that fix and redeploy quickly. Findings appear in the platform in real time, so developers can start on remediation before the test ends.
Best for: SaaS teams that release often and want to confirm API fixes within days. Our PTaaS providers list compares similar platforms.
4. NetSPI — Structured Three-Phase Testing Mapped To The OWASP API Top 10
NetSPI, headquartered in Minneapolis, runs expert-led API penetration testing aligned with the OWASP API Security Top 10, with focus areas in access control, injection, data exposure, resource consumption and misconfiguration. The work runs in three phases. Information gathering reviews the API catalog and documentation, analyzes architecture and business logic and confirms credentials and scope. Testing and evaluation runs as both anonymous and authenticated users, combines manual and automated assessment and checks access control across roles.
In the analysis and reporting phase, every finding gets CVSS v3.1 scoring, a mapping to the relevant OWASP API Top 10 category, business impact and remediation guidance, plus an executive summary. That mapping makes results easy to hand to auditors and developers alike.
Best for: Larger organizations with big API catalogs and complex role models that want consistent scoring across tests.
5. Packetlabs — API Testing Focused On High-Value Endpoints
Toronto-based Packetlabs tests REST, GraphQL, gRPC and custom or internal APIs, and its scope can include SOAP endpoints, microservices and third-party integrations. Its focus is on endpoints that handle money, data or privileges, where flaws such as broken object level authorization and excessive data exposure cause the most damage.
Findings are validated by testers rather than taken from tool output, and testers chain business logic edge cases to show real impact. Packetlabs also packages results as retest-ready documentation for SOC 2, ISO 27001, vendor reviews and security questionnaires, which helps B2B SaaS companies answer customer security reviews.
Best for: B2B SaaS and fintech teams that want testing focused on their highest-risk endpoints and evidence they can share with customers.
6. Triaxiom Security — Multi-Tenant Authorization Testing With A Free Retest
Charlotte-based Triaxiom Security runs API penetration tests that emulate real attackers and cover method and parameter fuzzing, injection, authentication bypass, authorization in multi-tenant setups, header and error message analysis and transport encryption. It does not exploit denial-of-service issues or run load tests, which is worth knowing if availability testing matters to you.
Pricing scales with API size and documentation quality, with its baseline estimate built around a small API of fewer than 50 well-documented endpoints. Proposals arrive within a few hours of scoping, most tests take one to two weeks, each report passes two QA rounds, and clients get one free retest within 90 days.
Best for: Multi-tenant SaaS companies that want tenant isolation tested through a predictable, well-documented process.
7. Schellman — API Testing From A Major Compliance Assessor
Schellman, based in Tampa, Florida, is a large attestation and compliance assessment firm that also runs penetration testing. Its API testers work directly against the API and proxy its traffic, manually altering requests to see whether the API can be pushed into unintended behavior. They map request and response flows to find attack paths, use fuzzing and injection payloads, test authentication and access control and check returned data for sensitive content.
Schellman is transparent about inputs and cost. It asks for detailed documentation such as Swagger or Postman collections plus credentials for authenticated testing, says API assessments take one to three weeks depending on endpoints and methods, and states that API tests start at no less than $14,500. Its testers hold certifications including OSCP, OSEP, OSCE and GPEN.
Best for: Companies that already use Schellman for SOC 2, ISO or PCI work and want API testing from the same firm.
8. Citadelo — Microservice And Token Testing For European Teams
Citadelo, with offices in Switzerland, Slovakia and the Czech Republic, tests REST, GraphQL and other APIs by simulating real-world attacks in line with the OWASP API Security Top 10. Its scope includes GraphQL introspection and query abuse and authentication through OAuth, OpenID Connect, JWT and API keys.
Citadelo also assesses communication between microservices, including identity and access management and trust between individual services, which is where many internal API flaws hide. Testers combine automated tools with manual testing and verify each finding by hand, with proof of exploitability and remediation guidance.
Best for: Central European companies with microservice architectures and token-based authentication.
Kroll’s API penetration testing looks for weaknesses in how APIs are designed, with attention to insufficient security configuration, authentication and authorization problems, HTTP header injection, input validation errors and insufficient logging. Kroll stresses that APIs often carry PCI and personal data, and its testers use expert inference to deduce back-end behavior rather than relying on front-end tooling.
Engagements follow a six-phase API testing process, with program managers and technical leads keeping work focused on the highest-risk areas. Kroll cites more than 100,000 hours of security testing per year, and it also offers an agile testing model tied to the development cycle for teams that want testing between releases.
Best for: Financial services, healthcare and other regulated organizations that want API testing from a large risk and incident response firm.
10. Astra Security — Platform-Led API Pentests With A Verifiable Certificate
Astra Security combines an automated scanner with pentests reviewed by its security engineers. Its API pentest follows the OWASP API Top 10, PTES and NIST, and Astra says it runs more than 150 tests per engagement, with static and dynamic API testing and a scanner updated with new CVEs.
Findings live in a dashboard with real-time support from engineers, and teams can request a rescan after patching. Astra also issues a publicly verifiable pentest certificate, which some startups use as evidence in sales and partner reviews.
Best for: Early-stage startups that want an affordable, platform-led API pentest and a shareable certificate.
How To Choose An API Penetration Testing Company
Do They Test Your API Style?
REST is standard, but GraphQL, gRPC and WebSockets need their own techniques. Blaze, Cobalt, Packetlabs and Citadelo name specific protocols. If a vendor only says “APIs,” ask how they handle yours.
How Do They Test Authorization?
Broken object level authorization is the most common serious API flaw. Ask whether testers use multiple accounts and roles, test tenant isolation and try to access other users’ objects, as NetSPI and Triaxiom describe.
What Do They Need From You?
Most firms want OpenAPI or Swagger files, Postman collections and test credentials for each role. Better documentation usually means lower cost and deeper coverage. Schellman and Triaxiom both tie pricing to documentation.
Is The Mobile Back End In Scope?
Many APIs exist to serve mobile apps. If so, consider testing both together. Our mobile app penetration testing companies list covers firms that test apps and their back ends.
What Does It Cost And How Are Retests Handled?
Published figures range widely, from Schellman’s floor of $14,500 to lower platform prices, and depend on endpoints and roles. Compare retest terms closely, from Cobalt’s seven-day unlimited retests to Triaxiom’s 90-day window. Our penetration testing cost guide covers what drives price.
Frequently Asked Questions
What Is API Penetration Testing?
API penetration testing is an authorized attack on your application programming interfaces to find flaws such as broken authorization, weak authentication, injection and excessive data exposure, and to show what an attacker could reach through them.
What Is The OWASP API Security Top 10?
It is OWASP’s list of the most critical API risks, including broken object level authorization, broken authentication and server-side request forgery. Most firms on this list map findings to it.
How Long Does An API Penetration Test Take?
Most take one to three weeks. Triaxiom cites one to two weeks for most APIs, and Schellman cites one to three weeks depending on the number of endpoints and methods.
Is An API Scanner Enough?
No. Scanners find known patterns but miss business logic and authorization flaws that need a human who understands roles and data. See vulnerability scanning vs penetration testing for more.
Conclusion
White Knight Labs suits teams that want APIs tested by hand alongside their web applications, Blaze Information Security suits teams running several API styles, and Cobalt suits fast-moving SaaS teams that retest often. NetSPI, Packetlabs, Triaxiom, Schellman, Citadelo, Kroll and Astra Security each fit specific needs, from large catalogs and multi-tenant SaaS to compliance-driven buyers and startups.
Whichever firm you choose, share good documentation, provide accounts for every role and agree on retest terms before testing starts. For broader options, see our top penetration testing companies list, or browse the full penetration testing hub.
