Is Your Contract Inside or Outside IR35?

You upload a contractor services agreement as a PDF or Word document, up to 5MB. The checker reads the text of the contract itself rather than asking you to summarise it, which matters: the wording of a substitution clause is the thing under assessment, and a questionnaire that asks "do you have a right of substitution?" cannot see whether the clause is real or decorative.

It then scores the contract across the six factors that UK employment status case law actually turns on, gives each one a score out of 100, and combines them into an overall probability that the written terms support an outside IR35 position. You get the score, the reasoning behind each dimension, the specific findings that drove it, a set of recommendations, and the case law that applies. The scan is free and does not require an account.

Personal service and substitution. Whether you are obliged to perform the work personally, or may send a substitute. A genuine, unfettered right of substitution is one of the strongest indicators of self-employment, but the checker looks at whether the clause is fettered by client approval, cost-bearing, or qualification requirements that make it unusable in practice.

Control. Who decides what is done, how it is done, when it is done, and where. Control over the manner of the work is weighted more heavily than control over the outcome, because a client specifying a deliverable is ordinary commercial behaviour, while a client directing your method looks like supervision.

Mutuality of obligation. Whether the client is obliged to offer work and you are obliged to accept it. This is the factor HMRC's CEST tool does not test at all, and following the Supreme Court's decision in HMRC v PGMOL (2024) it is also the factor whose meaning has moved most: mutuality can exist inside a single engagement through the wage-work bargain, without any obligation to offer future work.

Financial risk. Whether you can make a loss. Fixed-price work, rectification of defects at your own cost, providing your own equipment, and carrying your own insurance all point away from employment. Payment for time worked with no exposure points toward it.

Integration. How embedded you are in the client's organisation. Line management responsibility, appraisals, internal job titles, staff benefits and being held out to third parties as part of the client's team all count against an outside position.

In business on your own account. The overall picture. Multiple concurrent clients, your own branding, your own premises, marketing, and the ability to profit from sound management are what the courts describe as being in business on your own account, and this is the dimension the Court of Appeal leaned on in Atholl House.

The dimensions are not invented. They come from the line of cases that UK tribunals apply when deciding employment status, and the checker names the ones that bear on your particular contract rather than listing them generically.

• Ready Mixed Concrete v Minister of Pensions (1968) established the three-part test still in use: personal service, control, and whether the other terms are consistent with a contract of service.
• Autoclenz v Belcher (2011) established that where the written contract and the true agreement differ, the reality governs. This is why a strong contract score is necessary but not sufficient.
• HMRC v Atholl House (2022) confirmed that the wider picture of whether someone is in business on their own account forms part of the assessment, not merely the terms of the engagement in isolation.
• HMRC v PGMOL (2024) settled that mutuality of obligation can exist within a single engagement, and that a sufficient framework of control can be present even where day-to-day supervision is absent.

Our guides go through what a real right of substitution requires, why mutuality of obligation is the factor CEST omits, and which wins when your contract and your working practices disagree.

It does not determine your IR35 status, because no tool can. Status is determined by a tribunal applying the law to the facts of your engagement, and any product that tells you otherwise, including CEST, is describing a prediction rather than a ruling. What the checker gives you is a reasoned probability with its working shown, which is what you need in order to decide whether to push back on a determination, renegotiate a clause, or seek a paid human review.

It does not assess your working practices beyond what the contract says about them. If your agreement grants an unfettered right of substitution that your client would refuse in practice, the contract will score well and the reality will not. Following Autoclenz, the reality is what a tribunal would look at.

It is not insurance, and it is not regulated tax or legal advice. Where a human review or an insurance-backed opinion is the right answer, our guide to CEST alternatives names the firms that provide them and says plainly where they are a better fit than a self-serve tool.