---
title: "Release every resource you open · Agent Wranglers"
url: https://agentwranglers.se/playbook/architecture/errors-and-nulls/release-resources
updated: 2026-10-20
licence: "All rights reserved"
---

# Release every resource you open

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Required
- Chapter: [Errors and nulls](https://agentwranglers.se/playbook/architecture/errors-and-nulls)
- Rule: Close every file, connection, lock and handle with the language's scoped construct, so it is released on success and on error.
- How: Open the resource in a block that closes it on exit. Examples are `with` in Python, try-with-resources in Java, `using` in C#, `defer` in Go and `try` with `finally` in JavaScript. Never rely on the garbage collector to close it. Give pooled connections back the same way.
- Check: A linter fails on resources opened outside a scoped block. Examples are Pylint `consider-using-with`, Ruff `SIM115`, PMD `CloseResource` for Java and the .NET analyzer `CA2000`. A test that throws inside the block finds the resource closed.

Example:

```python
# Bad: an error in parse() leaves the file open
file = open("orders.csv")
orders = parse(file)
file.close()

# Good: the file closes even when parse() raises
with open("orders.csv") as file:
    orders = parse(file)
```

```java
// Good: try-with-resources closes the connection on every path
try (Connection connection = dataSource.getConnection()) {
    return orderRepository.load(connection, orderId);
}
```

```ts
// Good: finally gives the client back even when the query throws
const client = await pool.connect();
try {
  return await client.query('SELECT total FROM orders WHERE id = $1', [orderId]);
} finally {
  client.release();
}
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers architecture playbook: https://agentwranglers.se/playbook/architecture/errors-and-nulls/release-resources`.

- Previous: [Never swallow errors](https://agentwranglers.se/playbook/architecture/errors-and-nulls/never-swallow-errors)
- Next: [Await every async call](https://agentwranglers.se/playbook/architecture/errors-and-nulls/await-every-promise)
- [Errors and nulls](https://agentwranglers.se/playbook/architecture/errors-and-nulls)