Overview

Many modern content creation systems, such as WordPress and Notion, use a concept of ‘blocks’ to build content pages from. Users typically click on a big + button which allows them to insert one of any number of blocks of different types (e.g. paragraph, list, table, video). Pages built in this modular fashion can be as varied and interactive as the repertoire of available blocks. But these block systems are generally closed ecosystems. It is either (a) impossible for users to create new block types, or (b) impossible to use any block types created in one of these applications in another.

Even outside of content creation systems, web developers make use of a wide range of software libraries which implement web blocks: libraries to display, select, or edit particular types of data. These all have their own definition of what data they accept, how to send data into them, and how they send data back out. Making use of these libraries often requires learning a specific data interface and its idiosyncrasies.

This protocol aims to address both problems by defining a contract for data transfer between blocks and the applications which wish to make use of them, and how blocks describe the data they accept. If you adopt this protocol:

• Any block type from anywhere can be immediately embeddable in any compliant embedding application without any further documentation or configuration.
• Block types and the data they create and consume will not be tied to any specific implementation and may be easily ported between applications.
• Given a particular data structure, embedding applications can determine which block types are suitable for displaying and editing it.

The protocol enables this by specifying:

• the functions which block types should call to request or update data, and which embedding applications should provide to blocks,
• that blocks should express the data they accept in a machine-readable format.

Given a catalog of blocks built in compliance with the protocol, and embedding applications which know how to use them – which we can provide abstractions for – users can more easily find and use blocks to display and edit data structures they are interested in, be that tasks, tweets, or anything else.

A user could take a data structure, and search for blocks which can handle that data structure (or a useful portion of it) – whether they are a developer wanting to bundle a block with an application, or an end user of an embedding application which allows users to find and add new blocks themselves.

Blocks are as customizable as any other current component allows, but with a strong default setup, theme, and a predictable interface governed by this protocol, that provides plug-and-play functionality for data.

Terminology

Entity: an instance of data conforming to a schema, often corresponding to a thing in the real world.

Schema: a definition of a data structure, prescribing the shape of an entity (its properties). A schema might describe an entity which is linked to a family of blocks (e.g. the schema for Table blocks, which might have properties such as initialColumns), or other non-block entities (e.g. the schema for a Person, Movie, or List). There is no technical difference between the two, and either can described the data a block accepts (e.g. a MovieSummary block might accept a Movie).

Properties: the fields on a schema, what types of data are permitted as their values, and any other validation rules. Field types may be scalar (integer, string etc.), complex objects, collections (lists/arrays), or refer to another schema.

Block type: a definition and implementation – i.e. code – for a discrete component on a web page, which provides functionality for structured data (rendering it, editing it). A block type specifies the data it accepts via a schema in accordance with the spec.

Block: an instance of a block type inserted into a web page and supplied with data by an embedding application.

Block package: a collection of files making a block type available for use by embedding applications, including its source code and accompanying metadata.

Embedding application: an application which can take a block type and insert it in a web page, supplying the block with the structured data and dependencies it needs in accordance with the specification.

When capitalized, the words ‘MUST’, ‘MUST NOT’, ‘SHOULD’, ‘SHOULD NOT’, and ’MAY’ in this document are to be interpreted as described in IETF RFC 2119.

This document is focused on web software, but the principles of the contract between blocks and embedding applications can also be applied to other software.