Completeness clauses ("No oral ancillary agreements exist",
"No oral ancillary agreements were made", or "No oral ancillary agreements exist") are aimed at confirming the fact that the written contract contains all the provisions agreed between the parties regarding the subject matter of the contract, regardless of whether they are included in the contract as GTC or negotiated individually. The case law of the Federal Court of Justice has clarified that such clauses merely reflect the presumption of completeness and correctness of the written contractual document, which applies in any case, but leave it open to the contractual partner who wishes to invoke a deviating oral agreement to provide evidence to the contrary.

According to the BGH, a clause of completeness cannot give rise to an irrebuttable presumption that oral agreements do not exist, nor can it otherwise be inferred that the parties' agreements from the stage of negotiations leading up to the contract are no longer valid (see BGH, judgment of 03.03.2021 - XII ZR 92/19).

In addition, the BGH clarifies that such completeness clauses are invalid as general terms and conditions. It justifies this with the precedence of the individual agreement in accordance with Section 305b BGB, but also with Section 307 BGB and Section 309 No. 12 BGB. According to the latter standards, clauses in GTCs are also invalid if the user changes the burden of proof to the detriment of the other party to the contract, in particular by having the other party to the contract confirm certain facts.