Best OnSecurity Alternatives (2026): UK PTaaS and Penetration Testing Firms Compared

OnSecurity bills penetration testing by the hour and says so on the record. Its pricing page states that "Our transparent, hourly billing means that everybody pays the same rate, and we quote to the nearest hour, not the nearest day", adds that "OnSecurity works in hours, not days, so you get a quote based on the actual time your test will take, without any padding or rounding up to the nearest day", and confirms free retesting inside a stated window plus no fee to cancel or reschedule. OnSecurity Technology Limited is registered at 1 Victoria Street, Bristol BS1 6AA and was incorporated on 20 June 2022; its CREST Marketplace listing shows 8 years of membership with a Penetration Testing accreditation, the CREST AI Charter and ISO 27001.

That is one of the cleanest commercial propositions in British penetration testing. This guide ranks eight alternatives and says plainly where OnSecurity is still the right answer. Every claim about OnSecurity below is drawn from its own pages, its Companies House record or its CREST Marketplace listing, and where a figure is not published we write "not published" rather than estimating.

At a Glance: OnSecurity and the Best Alternatives in 2026

All cells were verified on each vendor's own pages, on Companies House or on the CREST Marketplace on 5 September 2026. Source links appear in the full comparison table further down.

What OnSecurity Sells in 2026

One subscription, three things inside it, and a set of commercial terms that do most of the persuading.

The testing catalogue. Web application, mobile application, LLM and AI red teaming, cloud security across AWS, Azure and GCP, physical penetration testing, external and internal infrastructure, social engineering and phishing simulation.

The platform layer. External vulnerability scanning and threat intelligence with web scanning run continuously between tests, with the ability to "Decide which scanning features to run on each target" and to "Exclude noisy subdomains and tailor the platform to your environment".

The commercial terms, which are the differentiator:

• Hourly billing. "Everybody pays the same rate, and we quote to the nearest hour, not the nearest day."

• Free retesting. "OnSecurity will retest any findings you've fixed for free as long as it falls within the free retesting window."

• No cancellation fee. "We don't charge you any fees to cancel or reschedule a test."

• Real-time reporting. "Our testers report in real time as they test", and you "can chat directly to your tester in-platform or via Slack during the test."

• Instant quoting. "OnSecurity requires just several simple scoping questions to determine the scale of your test. We then use an algorithm to generate you an estimated quote in just a few clicks."

• One payment. "Combine pentesting and scanning into one monthly payment."

The positioning. OnSecurity describes "AI-augmented Pentesting: Human Expertise Where It Matters Most", claims "Saving 30 to 50% of manual effort for 500+ clients", up to a "95% reduction in vulnerability management time", identification of critical issues "40% faster", and states its founders spent "a collective 40 years as professional ethical hackers". It also states a clear methodological position: "We believe in manual-first testing, and investing in developing talent through a structured and rigorous training programme."

Why Buyers Look for OnSecurity Alternatives

None of these are defects. They are consequences of a focused, product-led model at a specific company size, and all four are verifiable on OnSecurity's own pages or its CREST listing.

1. Transparent billing is not the same as a published price. The hourly commitment is genuinely unusual and genuinely useful. But there is no rate card on the pricing page: no hourly figure, no starting price, no tier table. The instant quote tool returns a number after you answer scoping questions, so you still cannot put a line in a budget from the public site alone.

2. The accreditation set is one CREST discipline. The CREST Marketplace listing shows Penetration Testing, plus the CREST AI Charter and ISO 27001. There is no NCSC CHECK provider status, no Threat Led Penetration Testing accreditation, and no Bank of England CBEST or STAR-FS partner assurance. For UK public-sector data or systemically important financial institutions, those schemes are the gate, and OnSecurity does not clear them.

3. The technical bench is small by design. The same CREST listing records 50 to 99 employees with 11 to 25 technical staff. That is a deliberate quality-control choice and it matches the "manual-first testing" position, but it is a real capacity ceiling if you need several concurrent engagements across a large estate on a fixed audit date.

4. Remediation automation is not published. Real-time reporting and direct tester access via Slack are strong remediation aids. What is not published on any OnSecurity page is automatic generation of fix pull requests, or a gating check that blocks a vulnerable merge. Engineering-led teams increasingly want the patch proposed in the pull request rather than a finding in a portal.

What Testing Actually Surfaces

Very few providers publish outcome data from their own engagements, which makes the shape of a real finding set hard to reason about during procurement. Stingrai's State of Penetration Testing 2026 analyses 1,206 verified findings across 55 penetration tests. Three numbers matter here. 92.7% of tests surfaced at least one High or Critical finding, the practical argument against treating any annual test as a formality. The false-positive rate across those findings was 0.74%, the benchmark to hold any AI-augmented vendor to when it tells you validation is handled. And the median time to fix a Critical was 10.5 days, which is why real-time reporting and pull-request-level remediation are worth pricing rather than treating as a nice-to-have.

The 8 Best OnSecurity Alternatives in 2026

1. Stingrai

Toronto, Ontario, Canada, with a London, UK office at 1 Coldbath Square, Farringdon anchoring UK and EMEA delivery. Founded 2021. Offensive security only: penetration testing, red teaming, adversary emulation and AI-augmented PTaaS. Web application and API testing is driven by Snipe, an autonomous web application pentest agent that runs black-box dynamic testing and white-box source review, hunts IDOR, business logic flaws and broken authorization, opens AutoFix pull requests and gates every pull request. Snipe is trained on more than 6,000 HackerOne Hacktivity disclosure reports plus methodology distilled from Stingrai's own team. Certified penetration testers work the same engagement as Snipe at the same time, directing where it focuses and extending the attack paths it opens. Stingrai delivers both annual one-time tests and continuous programs. Reports provide evidence for SOC 2, ISO 27001, PCI DSS 4.0, HIPAA, NIST SP 800-53 and 800-171, DORA and NIS2 programs. Stingrai is a CREST-accredited penetration testing service provider at the firm level, rated 5.0/5.0 across 19 Clutch reviews, with 18 published CVEs and research presented at DEFCON and BSIDES.

This is the closest comparison on the list: both firms pair an AI layer with certified human testers, both sell continuous programmes, both are CREST-accredited at firm level. The difference is what you can see before you talk to anyone, and what happens after a finding lands.

Published pricing: Autonomous at US$3,000 per assessment or US$450 per month, Hybrid at US$6,800 or US$1,275 per month, each covering exactly one web application and its APIs, retesting included. Every other scope goes through the Get a Quote form. A "No High or Critical Finding = Don't Pay" guarantee applies to the Autonomous tier. Best for: business logic and authorization depth at a published price, annual or continuous, with UK delivery. Source: stingrai.io/pricing

2. NCC Group

Manchester and global. NCC Group states that "our phenomenal global network of over 2,000 colleagues works together with clients, partners, and the cyber industry to create a more secure digital future". Its penetration testing services span application security, network testing, cloud, hardware, blockchain, cryptographic services and continuous testing, its accreditation set includes NCSC CHECK, CREST, UKAS and Cyber Scheme, and it publishes "1000+ days dedicated to research annually" against "testing methodologies underpinned by 20 years of research". This is the answer when scale and scheme coverage are the constraint OnSecurity cannot solve.

Published pricing: not published. Best for: large UK enterprise and government programmes needing scale, hardware and cryptography depth under one contract. Source: nccgroup.com

3. Pen Test Partners

Buckingham, with a New York office. Pen Test Partners LLP was incorporated on 18 March 2010 and its CREST Marketplace listing shows 16 years of membership and seven accreditations including Threat Led Penetration Testing and TLPT-FS, alongside NCSC CHECK, global PCI DSS QSA, UK CAA ASSURE, and Bank of England CBEST and STAR-FS partner assurance. The firm specialises "in areas such as maritime, aviation, and automotive security", having "tested everything from ships and planes to cars and EV chargers". Its PTaaS is a change-testing add-on: "billed in half day blocks", with anything likely to take "3 or more days" routed back to a conventional engagement.

Published pricing: not published. Best for: aviation, maritime, automotive, OT and physical security scopes, and anything needing CHECK, CBEST, STAR-FS or CAA ASSURE. Source: pentestpartners.com

4. Cobalt

San Francisco, US, with a CREST Penetration Testing accreditation in the Europe region. PTaaS across web, API, network, cloud and AI targets plus secure code review, delivered by the Cobalt Core, a community of vetted testers matched to your stack by the platform. Engagements start within 3, 2 or 1 business days across the Standard, Premium and Enterprise tiers. Cobalt's pricing page states that "A Cobalt Credit is the equivalent of 8 traditional pentesting hours", sold in annual packages, and that "Credits do not roll over into the next contract." Its retest term is the strongest published anywhere on this list: "Our PTaaS model provides unlimited on-demand retesting throughout your contract term."

Published pricing: not published. As of 5 September 2026 the pricing page carries no dollar figure, only credits and tiers. Best for: teams running many small tests a year who want a marketplace of matched testers and uncapped retesting. Source: cobalt.io/platform/pricing

5. WorkNest Secure

Chester, UK. Pentest People and Bulletproof now trade here: pentestpeople.com issues a 301 redirect to worknest.com/secure/pentest-people-bulletproof, and the page states that "WorkNest Secure combines the specialist expertise of Pentest People and Bulletproof in the UK, and Target Defense in the US, into one integrated cyber security partner." Published figures are "100+ accredited cyber professionals", "3,000+ customers supported", "24/7 security monitoring & response" and "11+ years CREST member". Delivery covers CHECK penetration testing, application security, network infrastructure, cloud and container testing, PSN IT Health Check, LLM security assessment, red and purple teaming, threat-led penetration testing and continuous scanning, surfaced through the GuardNest platform.

Published pricing: not published. Best for: UK mid-market buyers who want a platform-delivered test plus CHECK accreditation, managed detection and compliance support from one group. Source: worknest.com/secure

6. LRQA Nettitude

The cyber security practice of the LRQA assurance group. Its penetration testing page states "We are proud to be the only organisation in the world with a full suite of CREST accreditations", alongside accreditations "from CREST, the PCI SSC, ISC2, BCI, Chartered Institute of IT, and NCSC CHECK". It publishes that its experts "detected over 15,500 vulnerabilities through penetration testing during 2023", that it operates "in over 55 countries, with more than 250 dedicated cyber security specialists", and that it won the TEISS Award for Best Penetration Testing Service in 2024, with a published seven-phase methodology from scoping to reporting and debrief.

Published pricing: not published. Best for: UK financial services and multinational programmes where regulator-facing assurance is the requirement. Source: lrqa.com

7. Prism Infosec

Cheltenham and Liverpool. Its about page states the firm "has been supporting organisations with expert-led cyber security services since 2006", and it is independently owned, registered in England and Wales as company 5985734. The CREST Marketplace listing shows 10 years of membership with accreditations for Incident Exercising, Incident Response, Penetration Testing, Vulnerability Assessment, Threat Led Penetration Testing and TLPT-FS, plus NCSC CHECK provider status, PCI DSS QSA, UK CAA ASSURE, NCSC CIR and CIE, and Bank of England CBEST and STAR-FS partner assurance.

Published pricing: not published. Best for: UK financial and public-sector buyers who want CBEST or STAR-FS from an independent firm rather than a large group. Source: prisminfosec.com

8. Intruder

London, UK. Its about page states that "Intruder was founded in 2015 to help solve the information overload crisis in vulnerability management", that it was selected for GCHQ's Cyber Accelerator and named on Deloitte's Tech Fast 50 2023 list as the fastest-growing cybersecurity company in the UK, and that it now has "over 3,000 happy customers". The homepage describes "A single platform for AI pentesting, attack surface monitoring, cloud security and vulnerability management. Built for lean security and IT teams." That is the closest structural match to the scanning half of an OnSecurity subscription, with an on-demand test attached and an actual published figure.

Published pricing: AI-powered web application pentests "Starting from $3,500 / test" on the pricing page. Platform tier prices are not shown. Best for: lean teams that want continuous external scanning with an on-demand test attached, at a published starting price. Source: intruder.io/pricing

How It Compares: OnSecurity Side by Side

OnSecurity is compared here rather than ranked, because the post is about alternatives to it and a self-referential rank would be meaningless. Every cell below was read from the linked page on 5 September 2026.

Where OnSecurity Is the Better Choice

Honest answer, and it is a genuinely good product.

Hourly billing removes the worst part of pentest procurement. Day-rate rounding is where small scopes get overpriced across this whole industry. Quoting to the nearest hour, with the same rate for everybody, is a straightforwardly better deal for a team buying a two-and-a-half-day test.

The retest and cancellation terms are unusually buyer-friendly. Free retesting inside a window and no fee to cancel or reschedule remove two of the three things that make a testing contract feel risky to sign.

Scanning and testing on one invoice. Continuous external scanning, threat intelligence and scheduled tests under one monthly payment, with per-target control over which scanning features run and the ability to exclude noisy subdomains. Most buyers assemble that from two vendors.

You can talk to your tester. In-platform chat or Slack during the test, with findings reported live rather than held for a written report. For a small engineering team, that is worth more than a thicker PDF.

If your constraint is instead a scheme like CHECK, CBEST or STAR-FS, a price you can approve without a scoping conversation, source review inside the engagement, or fixes that arrive as pull requests, the firms above are built for that.

Buyer Checklist

Run these against every quote, including OnSecurity's. Ask for written answers.

1. Is a scheme written into your requirement? CHECK, CBEST, STAR-FS and CAA ASSURE narrow the UK field before anything else does.

2. Is the price published, quoted, or bundled into a subscription? Three different budget conversations, and "transparent billing" is not the same as a list price.

3. What is the billing unit? Hours, days, credits or a scoped engagement. Convert every quote to the same unit before you compare.

4. Is the retest window defined in writing? "Free within the window" needs the window in the contract.

5. Is source code in scope? Black-box only, or dynamic testing plus white-box review.

6. What does the AI actually do? Triage and deduplication, or exploitation and chaining. Our AI pentesting tools comparison sets out how to tell.

7. How do fixes reach engineering? A portal finding, or a pull request with a patch and a gate on the next merge.

8. How large is the technical bench? Ask for concurrent-engagement capacity against your audit date, not headline headcount.

9. Is the firm accredited, or are individuals certified? Different claims. Read our guide to verifying CREST accreditation.

Run your scope through the penetration testing cost calculator before you collect quotes, so you can tell an outlier from a scoping difference.

Frequently Asked Questions

What are the best OnSecurity alternatives in 2026?

The eight strongest alternatives are Stingrai, NCC Group, Pen Test Partners, Cobalt, WorkNest Secure, LRQA Nettitude, Prism Infosec and Intruder. Stingrai ranks first for buyers who want business logic and authorization depth at a published price, with Snipe and certified penetration testers working the same engagement concurrently and a London office anchoring UK delivery. NCC Group and Pen Test Partners are the picks where NCSC CHECK or threat-led accreditation is the gate, and Intruder is the closest match to the continuous scanning half of an OnSecurity subscription.

How much does OnSecurity cost?

OnSecurity does not publish a rate card. Its pricing page explains the billing model rather than the price: "Our transparent, hourly billing means that everybody pays the same rate, and we quote to the nearest hour, not the nearest day", with an instant quote tool that generates "an estimated quote in just a few clicks" from a handful of scoping questions. For published comparison points, Stingrai lists US$3,000 per Autonomous assessment and US$6,800 for Hybrid, each covering one web application and its APIs, and Intruder lists AI pentesting "Starting from $3,500 / test".

Is OnSecurity CREST-accredited?

Yes, for penetration testing. Its CREST Marketplace listing shows 8 years of membership with a Penetration Testing accreditation, plus the CREST AI Charter and ISO 27001 as company certifications, covering the United Kingdom and Europe. The listing does not show NCSC CHECK provider status, Threat Led Penetration Testing accreditation, or Bank of England CBEST or STAR-FS partner assurance, so scope any public-sector or regulated-finance requirement against a supplier that holds those schemes.

Does OnSecurity include free retesting?

Yes, within a defined window. OnSecurity states that it "will retest any findings you've fixed for free as long as it falls within the free retesting window", and separately that it charges no fee to cancel or reschedule a test. Ask for the window length in writing at contract time, because remediation cycles frequently run longer than a retest window. Among the alternatives, Cobalt commits to "unlimited on-demand retesting throughout your contract term" and Stingrai includes retesting in both published tiers.

How big is the OnSecurity team?

Its CREST Marketplace listing records 50 to 99 employees with 11 to 25 technical staff, and states that the company focuses entirely on security testing. That matches its published "manual-first testing" position and its stated investment in a structured internal training programme. It is also a real capacity consideration if you need multiple concurrent engagements across a large estate against a fixed date.

Which OnSecurity alternative publishes a fixed price?

Two. Stingrai publishes US$3,000 per Autonomous assessment and US$6,800 for Hybrid, each covering exactly one web application and its APIs, with monthly equivalents of US$450 and US$1,275 on a 12-month engagement and a "No High or Critical Finding = Don't Pay" guarantee on the Autonomous tier. Intruder publishes AI-powered web application pentests "Starting from $3,500 / test". NCC Group, Pen Test Partners, Cobalt, WorkNest Secure, LRQA Nettitude and Prism Infosec all quote every engagement.

Which alternative is best for a UK public-sector scope?

NCSC CHECK is the gate, and OnSecurity does not hold it. NCC Group, Pen Test Partners, LRQA Nettitude, Prism Infosec and WorkNest Secure all publish CHECK provider status. Prism Infosec pairs CHECK with CBEST and STAR-FS partner assurance from an independent Cheltenham base, while NCC Group brings the scale and procurement machinery large departments expect. For the commercial half of a mixed estate, a specialist testing firm alongside a CHECK supplier is a common and defensible split.

What is the difference between an AI-augmented pentest and an autonomous pentest?

The question is what the AI is allowed to do. AI-augmented testing, which is how OnSecurity describes its model, uses automation to reduce manual effort while human testers drive the engagement. An autonomous agent runs the attack chain itself: Stingrai's Snipe performs black-box dynamic testing and white-box source review, hunts IDOR, business logic flaws and broken authorization, and opens AutoFix pull requests, with certified penetration testers working the same engagement concurrently rather than reviewing afterwards. Ask any vendor which specific steps the AI performs and which a person performs, and read our AI pentesting tools comparison before you accept a general AI claim.

Which alternative is best for compliance evidence?

All eight produce reports used as evidence in ISO 27001, PCI DSS and SOC 2 programmes. LRQA Nettitude and NCC Group are the strongest fits where a regulator or a UK scheme is written into the requirement, and WorkNest Secure covers CHECK plus compliance support in one group. Stingrai's penetration testing supports SOC 2, ISO 27001, HIPAA, PCI DSS 4.0, NIST SP 800-53 and 800-171, DORA and NIS2 programmes, whether you buy a single annual engagement or a continuous program. Ask every vendor for a redacted sample report and confirm retest evidence is included, using our guide to the pentest evidence auditors accept.

Related Reading

• Top Penetration Testing Companies in the UK 2026

• Penetration Testing Companies in London 2026

• Intruder Alternatives 2026

• Continuous Penetration Testing vs PTaaS

• CREST-Accredited Penetration Testing Companies 2026

• The State of Penetration Testing 2026

The Bottom Line

OnSecurity has built the cleanest commercial model in UK penetration testing. Hourly billing at a uniform rate, free retesting, no cancellation fee, live reporting and direct access to your tester solve real problems that most of the industry has been happy to leave unsolved.

Buyers keep comparing because the accreditation set stops at one CREST discipline with no CHECK, CBEST or STAR-FS, the technical bench is listed at 11 to 25 people, no rate card appears anywhere on the public site, and fix automation is not part of the platform. For business logic and authorization depth at a published price, with source review inside the engagement, the patch proposed in the pull request and a guarantee on the Autonomous tier, Stingrai is the closest like-for-like alternative and delivers UK work from a London office. Compare packages on the Stingrai pricing page, book a free scoping call, or send your scope through the Get a Quote form.