# OP\_Return The data representing Runes is stored within the OP\_RETURN field of a Bitcoin transaction. OP\_RETURN is an operation code (opcode) from Bitcoin’s scripting language that enables users to embed arbitrary data onto the blockchain. The official limit for data stored in an OP\_RETURN field is 80 bytes, providing a dedicated space for storing information related to Runes. The [official Runes documentation](https://docs.ordinals.com/runes.html) provides detailed explanations and guidelines on the specific usage and formatting of OP\_RETURN outputs for representing Runes data. This documentation serves as a valuable resource for developers and users interested in understanding and implementing the Runes Protocol within the Bitcoin ecosystem. By utilizing the OP\_RETURN field, the Runes Protocol can seamlessly integrate [fungible](https://en.wikipedia.org/wiki/Fungibility) token data into regular Bitcoin transactions, without modifying the core Bitcoin protocol or introducing external dependencies. This approach aligns with the ethos of Bitcoin's decentralized and open-source nature, allowing for innovative applications and use cases to be built on top of the existing infrastructure. --- # 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://book.runesterminal.io/3.-runes/op_return.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.