In theory, a real estate contract can be written on a napkin. However, there are various factors that need to be considered before determining the legality of such a contract.

Firstly, it is important to note that a real estate contract is a legally binding agreement between two or more parties, which outlines the terms and conditions of a real estate transaction. This means that the contract must meet certain legal requirements to be enforceable in a court of law.

One of the requirements for a real estate contract is that it must be in writing and signed by all parties involved. While it is true that a napkin can be used as a writing surface, it may not provide enough space to include all the necessary details of the transaction.

Additionally, the use of a napkin as the writing surface may raise concerns over the authenticity of the contract. It may be difficult to prove that the contract was written and signed by the parties involved, especially if there is no witness present.

Furthermore, certain real estate transactions may require specific legal language or terms that may not be easily conveyed on a napkin. For example, a contract for the sale of a property may require specific clauses related to the condition of the property, the closing date, and financing arrangements, which may be challenging to include on a napkin.

It is also worth noting that certain jurisdictions may have specific legal requirements for the format and content of a real estate contract, which may not be met by a contract written on a napkin.

In conclusion, while it is theoretically possible to write a real estate contract on a napkin, it may not be a practical or advisable option. To ensure the validity and enforceability of a real estate contract, it is best to consult with a qualified legal professional and use a formal written contract that meets all the necessary legal requirements.