---
title: "tool si.read.why"
description: "any unit: the chain of reasons, from this unit back to its first cause."
section: reference
address: /reference/tools/si-read-why
contract: 0476e35e6e275db5
---

# tool si.read.why

any unit: the chain of reasons, from this unit back to its first cause.

[figure: Over MCP, si.read.why takes WhyInput and returns a card whose body is WhyAnswer.]

the chain of reasons, from this unit back to its first cause. The call needs the read grant at the user rung.



| | |
|---|---|
| input | [WhyInput](/concepts/whyinput) |
| result | a card whose body is [WhyAnswer](/concepts/whyanswer) |
| read-only | yes |
| destructive | no |
| card address | `ui://scale-intelligence/cards/WhyAnswer` |
| HTTP route | [`/v1/read/why`](/reference/read/why) |





| field | type | required | note |
|---|---|---|---|
| `unit` | [UnitRef](/concepts/unitref) | yes |  |