---
title: "The registers, and the contract crate"
description: "The registers, and the contract crate: the 2 calls this system serves, each a route of the API and a tool of the MCP server, at contract 0476e35e6e275db5."
section: systems
address: /systems/02-the-registers-and-the-contract-crate
contract: 0476e35e6e275db5
---

# The registers, and the contract crate

The registers, and the contract crate: the 2 calls this system serves, each a route of the API and a tool of the MCP server, at contract 0476e35e6e275db5.

[figure: The registers, and the contract crate: 2 calls of the contract, by family.]

# The registers, and the contract crate

The 2 calls below are the whole of this system on the wire: each is one route of the API and one tool of the MCP server, with one typed input, one card as its answer and one refusal shape. Every answer carries its foot: what was read, the population and the control.

## The calls



| tool | route | takes | gives |
|---|---|---|---|
| [si.read.register](/reference/tools/si-read-register) | [POST /v1/read/register](/reference/read/register) | its name, and a version or *current* | its rows, and the hash |
| [si.read.registered](/reference/tools/si-read-registered) | [POST /v1/read/registered](/reference/read/registered) | a register and a name | the row, or nothing |