> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lerian.studio/llms.txt
> Use this file to discover all available pages before exploring further.

# The outside world

> The doorway between your Ledger and the world outside, and how you prove your records match reality.

Everything so far has lived neatly inside your Ledger. But money doesn't stay inside — it arrives from banks, card networks, and other systems, and it leaves to them too. So how does a self-contained Ledger connect to the world outside? And once it does, how do you *prove* your records still match what really happened out there? Two ideas answer this, and they're really one story.

Picture a building with a single front door. Everyone and everything coming in or going out passes through it. The door doesn't store anything itself — it just marks the boundary between inside and outside. Your Ledger has a door like this, and it's worth understanding before you trust the numbers on either side of it.

## External accounts: the doorway to the outside

***

An **external account** is the doorway between your Ledger and the world beyond it — banks, card networks, other systems. Money entering your Ledger comes *from* an external account; money leaving goes *to* one. Every crossing of your boundary passes through it.

Here's the part that surprises people: an external account can look **negative**, and that's correct — not a bug. The external account mirrors the value that crossed your boundary. When R\$100 flows *in* to a customer, that value had to come *from* somewhere outside — so the external account is debited R\$100 and shows the outflow from the world's side. It's simply the other half of the double-entry, recorded at the edge.

<Note>
  Think of the building's front door again. The external account is that door. A "negative" balance there doesn't mean money is missing — it's a faithful record of how much value has crossed the boundary, seen from the outside in.
</Note>

```mermaid mermaid theme={null}
flowchart LR
  E["External account<br/>(the doorway)"] -->|"+ R$100 in"| A["Customer account<br/>(inside the Ledger)"]
  classDef bal fill:#fff8e1,stroke:#f4b400,color:#333;
  class A bal;
  classDef ext fill:#eef2ff,stroke:#6366f1,color:#333;
  class E ext;
```

## Reconciliation: proving the books match reality

***

Once you have a boundary, you need to check that what you recorded inside matches what the outside world recorded. That check is **reconciliation**: proving your internal records line up with external records — bank statements, processor reports, settlement files.

You compare the two, line by line, and confirm they agree. When they don't, reconciliation is how you catch it:

* **Missing** movements — something happened outside that your Ledger never recorded.
* **Duplicated** movements — the same thing recorded twice.
* **Mismatched** movements — amounts or details that don't line up.

When do you do it? It depends on your business — some reconcile **continuously** as records arrive, others at the **end of each day**. Either way, it's the natural counterpart to having a boundary: the moment you connect to the outside world, you take on the job of proving the two sides still agree.

<Note>
  Reconciliation is like **counting the till against the receipts** at the end of a shift. The cash drawer is your Ledger; the receipts are the outside record. Counting them against each other proves the books match what actually happened — and flags anything that doesn't.
</Note>

## In short

***

* An **external account** is the doorway between your Ledger and the outside world — money in comes from it, money out goes to it.
* It can look **negative**, and that's correct — it mirrors the value that crossed your boundary, the other half of the double-entry.
* **Reconciliation** is proving your internal records match external ones (bank statements, processor reports).
* It catches **missing**, **duplicated**, and **mismatched** movements, run **continuously** or at **end of day**.

<Note>
  **See it in Lerian**

  See these ideas in practice: [Transactions](/en/midaz/transactions) and the [Glossary](/en/glossary).
</Note>