The Best API Penetration Testing Companies UK
The best UK API penetration testing companies in 2026 are CREST-accredited firms with proven OWASP API Security Top 10 methodology, BOLA-focused authorisation testing across every tenant and role, and dedicated REST and GraphQL coverage rather than a generic web app check. This guide compares 7 leading providers: Precursor Security, NCC Group, Pen Test Partners, Redscan (Kroll), JUMPSEC, OnSecurity, and Fortbridge, on criteria any buyer can check independently.
Seven CREST-accredited UK API penetration testing companies compared on the criteria that actually matter to buyers: OWASP API Top 10 depth, BOLA-focused authorisation testing, verifiable accreditation, and pricing you can see before a sales call.
We are Precursor Security, and we have ranked ourselves first on this list.
Rather than pretend otherwise, we publish the selection criteria in full, describe every competitor fairly, and link the independent CREST member directory so you can check our working. The firms below are genuinely good at API testing. The differences are in delivery model, transparency, and who each firm serves best.
Seven firms, side by side
| Provider | CREST status | Pricing published | From |
|---|---|---|---|
| 1. Precursor Security | Pen Test + VA + SOC | Yes | From £3,750 (scoped with the web application test) |
| 2. NCC Group | Member firm | No | On application |
| 3. Pen Test Partners | Member firm | No | On application |
| 4. Redscan (Kroll) | Member firm | No | On application |
| 5. JUMPSEC | Member firm + NCSC CHECK | No | On application |
| 6. OnSecurity | Member firm | No | Instant quote via platform |
| 7. Fortbridge | Member firm | No | On application |
Verified against each company's public website, September 2026. "No" means we could not find a published rate; it does not mean the firm lacks one.
The 7 best UK API penetration
testing companies in 2026
1. Precursor Security
Precursor holds triple CREST accreditation across Penetration Testing, Vulnerability Assessment, and Security Operations Centre services, a combination held by fewer than 70 firms worldwide. Every API engagement tests against all ten OWASP API Security Top 10 (2023) categories, with Broken Object Level Authorisation (BOLA) probed across every endpoint and multi-tenant object hierarchy, alongside REST, GraphQL and SOAP protocol-specific test sequences. Provide an OpenAPI specification or Postman collection and scoping is confirmed within 24 hours; most engagements cover 20 to 100 endpoints across 3 to 5 days. A retest is included, and every tester is a UK-based, DBS-checked employee. Findings feed directly into SOC detection rules for clients running both services.
Trade-off: A mid-market specialist rather than a global enterprise brand, and very large or highly complex multi-protocol API estates are scoped individually rather than quoted from a single published number.
2. NCC Group
NCC Group is one of the largest security consultancies in the world, headquartered in Manchester, with a deep research pedigree and the bench depth to staff large, multi-application testing programmes. For a FTSE-100 estate running dozens of REST services and legacy SOAP interfaces across multiple regions, few firms can match the capacity.
Trade-off: Engagement model and pricing are built for enterprise procurement. Costs are on application.
3. Pen Test Partners
Pen Test Partners are the UK's best-known specialists in embedded and operational technology. When a connected device talks to a cloud back end, the API layer between device and platform sits inside their standard scope alongside the hardware and firmware itself, and their public research is consistently excellent and widely cited.
Trade-off: A pure enterprise SaaS REST or GraphQL API with no hardware component is not their headline strength. Pricing on application.
4. Redscan (Kroll)
Redscan, now part of Kroll, pairs a large practitioner organisation with strong client review scores and the backing of a global incident response and forensics business. For organisations that want their API tester, their IR retainer, and their forensics provider under one roof at enterprise scale, the Kroll relationship is the draw.
Trade-off: Pricing on application, and the engagement model leans enterprise.
5. JUMPSEC
JUMPSEC holds NCSC CHECK status alongside CREST membership, which makes them a strong choice for PSN-connected services and government platforms that mandate CHECK delivery for authenticated API testing. Named private sector clients and published case studies add useful proof.
Trade-off: Pricing on application.
6. OnSecurity
OnSecurity runs a platform-first, pentest-as-a-service model with instant online quoting and quick scheduling for API and web application testing, and carries strong review scores on G2. For a SaaS platform whose API is the product, booking testing this week with minimal procurement friction is the appeal.
Trade-off: Quotes are generated through their platform rather than published as a rate card, and the model is optimised for smaller, repeatable API scopes.
7. Fortbridge
Fortbridge is CREST-accredited for penetration testing and publishes a dedicated API penetration testing service alongside a public vulnerability research blog documenting real-world findings, including GraphQL introspection exposure and BOLA in production fintech APIs. Engagements are led by consultants with 10 to 20 years of offensive experience rather than junior staff, which suits organisations that want depth on a smaller number of complex, high-value API endpoints.
Trade-off: Pricing is discussed on a discovery call rather than published as a rate card, and the model is built for depth on complex APIs rather than high-volume, repeatable PTaaS throughput.
How we ranked them
Six criteria specific to what an API penetration test actually needs to cover, each something a buyer can verify without taking anyone's word for it.
All ten OWASP API Security Top 10 (2023) categories tested, with Broken Object Level Authorisation treated as the priority: it is the most common and most exploitable class of API vulnerability, and testing it properly requires a valid, authenticated session, not an anonymous scan.
Every user role and tenant defined in scope, then tested against every other role and tenant for horizontal and vertical privilege escalation. A flat, single-account test cannot find the authorisation flaws that only appear between users.
Protocol-aware test sequences, not generic checks. GraphQL introspection and nested query abuse, REST verb tampering and shadow endpoint discovery, and webhook target validation for server-side request forgery.
An OpenAPI specification or Postman collection is used to understand the data model and manually probe business logic, not just to seed an automated fuzzer. Fuzzing finds crashes; manual testing finds the authorisation and logic flaws fuzzing cannot reason about.
Company accreditation in the CREST directory, and individual tester certification, not just an organisational badge on a website.
Whether verification of your fixes is included, and whether the firm connects API findings into ongoing monitoring rather than treating the test as a one-off annual PDF. See our approach to closed-loop security.
Red flags when choosing
an API pentest company
Whichever firm you choose, including us, walk away if you see these.
A scanner pointed at Swagger sold as an API pentest
Running an automated tool against your OpenAPI/Swagger definition and repackaging the output as a penetration testing report will find missing headers and outdated libraries, not authorisation flaws. Ask directly how many days of manual, authenticated testing are included, and by whom.
Unauthenticated-only testing
Testing an API only as an anonymous, logged-out caller cannot find BOLA, the single most common and most damaging API vulnerability, because BOLA requires a valid authenticated session to demonstrate. If a quote does not specify authenticated, role-based testing, it is not testing the risk that matters most.
No multi-tenant or role matrix
A proper API test defines every user role and tenant in scope, then tests each object and endpoint across every combination: user A trying to reach user B's data, a standard user trying to reach an admin function. A quote that treats the API as a single flat surface has not planned for authorisation testing at all.
GraphQL excluded from scope
GraphQL introduces its own risk surface: introspection exposure, deeply nested queries used for denial of service, and batched mutation abuse. A provider whose methodology only lists REST checks either cannot test GraphQL or has not thought about it, and either way your GraphQL endpoints go untested.
No retest
An API pentest without verification of your fixes is half a service. If the retest is sold back to you as a separate, second engagement, your remediation evidence for auditors and enterprise customers costs double.
Opaque pricing
A firm that cannot indicate its day rate or a from-price before a discovery call is optimising for deal-size discovery, not your budget. UK CREST day rates for API testing sit in the same £1,000 to £1,500 band as other manual testing; anyone refusing to anchor near that range is hiding something.
UK API penetration testing prices in 2026
Across the market, CREST-accredited API testing runs at the same £1,000 to £1,500 per consultant day as other manual testing disciplines. At Precursor's published rate of approximately £1,200 per day, API testing is scoped alongside the web application test, from £3,750 combined for a typical 20 to 100 endpoint estate over 3 to 5 days, with complex multi-protocol estates covering REST, GraphQL and SOAP together scoped individually above that.
Full cost guide with worked examplesRelated pages worth reading next.
API security testing
CREST-accredited REST, GraphQL and SOAP testing: BOLA, mass assignment, broken authentication.
See the serviceWeb application penetration testing
Pair API testing with full front-end coverage when a web app drives the API.
See the servicePenetration testing cost guide
UK day rates, scope multipliers, and worked examples by engagement type.
See cost guideClosed-loop security
How offensive API findings feed defensive monitoring instead of sitting in a PDF.
See the modelBest web application penetration testing companies UK
The wider ranking for full application testing, front end included.
See the full rankingBest penetration testing for SaaS
Multi-tenant considerations for SaaS platforms choosing a testing provider.
See the SaaS guideCompare us against anyone on this list.
Fixed pricing published before you call. A written quote within 24 hours of a scoping conversation. Retest included.
Choosing an API pentest company
The questions buyers ask most when comparing UK API testing providers.
Most API penetration tests cover 20 to 100 endpoints across 3 to 5 days of manual testing, at the CREST-accredited market rate of roughly £1,000 to £1,500 per consultant day. At Precursor, API testing is delivered as part of the web application testing practice and scoped with it, from £3,750 combined at approximately £1,200 per day. Complex multi-protocol estates covering REST, GraphQL and SOAP together are scoped individually. Most firms on this list price API testing on application.
A web application pentest covers the full application, including the browser-facing UI, session handling and the APIs the front end calls. An API pentest ignores the UI entirely and interacts directly with REST, GraphQL or SOAP endpoints, focusing on authorisation, data exposure and business logic at the protocol level. When a web front end and its API are built together, testing both in one engagement gives fuller coverage than testing either in isolation; most CREST-accredited firms, including the ones compared here, can scope a combined engagement.
BOLA (Broken Object Level Authorisation) is the number one category in the OWASP API Security Top 10. It occurs when an API lets an authenticated user access or modify another user's data, an invoice, a message, a profile, simply by changing an ID in the request, without any additional privilege. It is the most common and most exploitable class of API vulnerability, and it is invisible to unauthenticated scanning because it requires a valid, authenticated session to test properly. Any provider that only tests APIs unauthenticated will miss it.
Scoping is based on endpoint count, HTTP methods, authentication complexity and the number of distinct user roles or tenants that need testing, not page count or URL count. Providing an OpenAPI/Swagger specification or a Postman collection allows for a comprehensive white-box test covering every documented endpoint; without documentation, testing is still possible but coverage may be limited to endpoints discoverable through the front end. Most engagements cover 20 to 100 endpoints across 3 to 5 days, and a fixed quote should follow within a day or two of receiving the specification.
Based on verifiable CREST accreditation, API-specific methodology, and pricing transparency, the leading UK API penetration testing companies are Precursor Security, NCC Group, Pen Test Partners, Redscan (Kroll), JUMPSEC, OnSecurity, and Fortbridge. Each suits a different buyer: Precursor for published fixed pricing and OWASP API Top 10 depth, NCC Group and Redscan for enterprise scale, Pen Test Partners for hardware-adjacent APIs, JUMPSEC for CHECK-mandated public sector work, OnSecurity for fast SaaS turnaround, and Fortbridge for senior-led depth on complex GraphQL and REST estates.