# Covenants In Mel's [data model](/concepts/data-model.md), every coin/UTXO is locked by a *covenant*, or a program that constrains what sort of transaction can spend it. Common covenants include: * Checking that a transaction is signed by a particular public key * Checking that a transaction is signed by some subset of keys (a *multisig* covenant) * Encoding arbitrary stateful logic using *self-propagating* covenants On the blockchain level, covenants are written in the low-level [MelVM](/resources/melvm-spec.md) language, but in practice covenants are programmed using the high-level [Melodeon](https://melodeonlang.org/) language. More info on specific programming patterns can be found in the [Melodeon guide](https://guide.melodeonlang.org/). --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.melproject.org/concepts/covenants.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.