JSON-RPC

JSON-RPC is like a letter format that different programs use to send commands to each other across a network. If you write a letter any old way, the recipient won't understand what you're asking for. So JSON-RPC is an agreed-upon format where you fill in fixed fields on the envelope — who's sending it, what the request is, and a request number — and the contents inside are written using JSON, a notation that's easy for humans to read too.

For example, if Program A wants to ask Program B to read a file, it writes down the name of the request along with any needed information, and sends it following this format. Program B replies with the result or an error using the same format. Even if the programs are built by different companies, as long as they both follow this format, they can understand each other.

As the article describes, for a cloud-based AI agent to call a tool on your local computer, there needs to be a bridge in between that converts messages into this format. Converting these JSON-RPC messages is one of the jobs that bridge does.

The article explains that AWS's bridge "translates between native messaging formats and raw MCP JSON-RPC messages." Here, JSON-RPC isn't a concept unique to AI services — it's a general-purpose communication standard that many kinds of software have long used to exchange remote commands. Modern AI connection technologies like MCP (a standard way of linking programs and tools together) also exchange messages on top of this standard.