> ## 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 outside world — how external accounts work and how reconciliation proves your records match reality across systems.

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>