An estoppel certificate is a signed statement, usually by a tenant, confirming key facts about a lease: that it is in effect, its dates and rent, what deposits are held, what concessions exist, and that neither party is in default.
Why buyers and lenders require them. A rent roll is the seller’s summary. An estoppel is the tenant’s own statement, and having made it the tenant is generally precluded from later asserting something inconsistent to the party who relied on it. In a portfolio purchase it is the only reliable way to learn what side agreements exist.
What to look for in a returned certificate. Exceptions written in by the tenant are the point of the exercise — an unrecorded option to renew, a rent abatement agreed by email, a landlord repair obligation outstanding. A certificate returned with handwritten qualifications is doing exactly what it is for.
Practical mechanics. Most leases obligate the tenant to deliver one within a stated period of request; the obligation is frequently ignored, and enforcement is slow. Build time into the transaction. Some leases deem the facts confirmed if the tenant fails to respond, which is worth negotiating into new leases.
Related. A subordination, non-disturbance and attornment agreement addresses what happens to the tenancy if the landlord’s lender forecloses, and is usually requested at the same time.