The most important source of information about a residential tenant’s rights and a landlord’s responsibilities is the written lease agreement. Some landlords prefer oral agreements, but it is more common for them to require the tenant's signature on a written lease—and a written lease protects the tenant more than an oral agreement. Be sure to read the lease carefully before you sign it.

A residential landlord’s ability to charge late fees generally depends on the specific language in the written lease agreement; the state’s landlord-tenant laws that may limit the amount of late fees the landlord can charge and the circumstances in which they can be charged; and the state's contract law.

Contract law in most states recognizes an implied duty of good faith and fair dealing between parties to a contract, and a residential landlord who charges late fees because the tenant is an hour late paying the rent may be in breach of the landlord’s implied duty of good faith and fair dealing—unless, for example, the lease agreement specifies an hour (12:00 p.m.) of the day by which rent is due and states that time is of the essence.

In Delaware, the written lease agreement is indeed a crucial document outlining the rights of residential tenants and the responsibilities of landlords. Delaware law requires that all agreements for the rental of a residential property for a term less than one year must be in writing to be enforceable. A written lease provides clarity and serves as evidence of the terms agreed upon by both parties, offering more protection than an oral agreement. Tenants should thoroughly review and understand the lease before signing. Regarding late fees, Delaware's Residential Landlord-Tenant Code does allow landlords to charge late fees, but they must be reasonable and specified in the lease agreement. The law caps late fees at 5% of the monthly rent. Additionally, Delaware recognizes the implied covenant of good faith and fair dealing in contracts, which means that landlords are expected to act fairly and not use the lease terms to take advantage of tenants. For instance, charging a late fee for rent that is only an hour late without a clear stipulation in the lease that time is of the essence would likely be seen as a breach of this duty. It is important for both landlords and tenants to be aware of these legal provisions to ensure a fair and lawful tenancy.