# `visibility.public_reaches_private`

Public declaration's signature names one that isn't public.

Area 1, [Project layout and modules](../topics/project-layout-and-modules.md); not declinable; the next step is usually the agent's.

Everything a public declaration's signature names is public too (area 11),
since whoever uses it
has to build or handle it: a public action's parameters, result and failures,
a public type's fields, a public library's functions' signatures. A type in
`shared/` or the standard library is everyone's already:




```jadpo
use billing/types { Amount }

public action charge(amount: Amount) -> Unit {}
```

```text
error: `charge` is public, but `Amount` isn't
 --> domains/billing/actions/charge.jadpo:3:30
  |
3 | public action charge(amount: Amount) -> Unit {}
  |                              ^^^^^^ a type only domain `billing` sees
  reason: Whoever uses a public action has to build or handle what its signature names, so everything it names is public too; `Amount` is a type in `domains/billing/types/amount.jadpo` that only domain `billing` sees.
  next: Mark `Amount` `public`, or keep it out of `charge`'s signature (agent)
  rule: visibility.public_reaches_private
  help: https://jadpo.dev/docs/errors/visibility.public_reaches_private

check failed: 1 error, 4 files
```