# Introduction to Mercury's Cloud and the Zephyr Stack {% hint style="warning" %} Note that this section is currently minimal and still a work in progress. {% endhint %} As mentioned in the quickstart, the Zephyr virtual machine powers the Mercury cloud execution environment. At its core, Zephyr is a WebAssembly VM like the Soroban VM, but with the focus on working with network data and interacting with databases. At the low level it is therefore structured as a messaging protocol between the guest and the host. These *"messages"* are in fact database writes/reads envelopes and requesting ledger reads and web requests. All while the guest environment has the liberty of doing whatever logic is described in the program's code with the data it sends to and receives from the host environment. The functions on which the guest relies upon to communicate with the host are the so-called host functions. Because working directly with these functions becomes low level and difficult, we have developed the `zephyr-sdk` crate. It currently exists only in rust, but if we see the potential for other SDKs to bring more value in the ecosystem zephyr programs could potentially be written in any language that compiles to WebAssembly. --- # 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.mercurydata.app/zephyr-full-customization/learn/introduction-to-mercurys-cloud-and-the-zephyr-stack.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.