Is there a rule on how much of my pay must be basic salary in the UAE?

For most private-sector jobs onshore there is no fixed legal ratio dictating how much of your package must be basic salary, so the recruiter is right that allowance-heavy splits are common and lawful. But your friend is right that the split matters. End-of-service gratuity is calculated on your basic wage only, so a low basic directly shrinks what you collect when you eventually leave, and over several years the difference can be substantial. Other calculations and assessments, from certain leave-related payments to bank lending and some visa criteria, can also key off the basic figure or how the package is documented. The split is set by the contract you sign and register, so treat it as a negotiation point rather than a formality: ask for a higher basic even at the same total package, and make sure the contract registered with MOHRE or your free zone matches the offer letter. Get the final breakdown in writing before you accept, because changing it later requires the employer's agreement. A lawyer experienced in UAE employment contracts can model what the split means for your end-of-service benefits before you sign.