---
title: "Report errors with line and column"
url: https://recursiveai.org/oneyaml/csharp/cookbook/errors-with-line-and-column/
description: "Catch OneYaml’s YamlException in C# and report the line, column, category and path of a syntax error, a duplicate key or a value that doesn’t fit its type."
version: "1.2.1"
---

# Report errors with line and column

Validate a YAML file and say exactly what’s wrong and where. Every OneYaml error is a `YamlException` with the position, a category to switch on and, for a value, the JSON Pointer path to it.

```csharp
using OneYaml;

// Malformed YAML: line, column and a category to switch on.
Report(() => YamlDocument.Parse("name: web\nports: [80, 443\n").Dispose());

// A duplicate key.
Report(() => YamlSerializer.Deserialize<object>("name: web\nname: api\n"));

// A value that doesn't fit its type: the path to it, too.
Report(() => YamlSerializer.Deserialize<Config>("port: 99999\ndebug: yes\n"));

static void Report(Action read)
{
    try
    {
        read();
    }
    catch (YamlException e)
    {
        Console.WriteLine($"{e.Line}:{e.Column} {e.Category} {e.Path}");
        Console.WriteLine($"  {e.Message}");
    }
}

record Config(ushort Port, bool Debug);
```

```text
3:1 Syntax 
  Expected ',' or ']' in the flow sequence. (line 3, column 1)
2:1 DuplicateKey /name
  The key 'name' appears twice in the mapping. (line 2, column 1, path /name)
1:7 Binding /port
  The number '99999' is outside the range of an unsigned 16-bit integer. (line 1, column 7, path /port)
```

## Good to know

- `Line` and `Column` are 1-based; `Offset` is the position in the input. `Path` is the JSON Pointer to the value, when there is one.
- **Switch on `Category`**, not on the message: `Syntax`, `DuplicateKey`, `Binding`, `Limit`, `PatchTest`, `RefusedAlias` and the others.
- `Message` already includes the position and path, so it reads well in a log. Set `SourceName` in the options to put the file name in front of it.
- A read stops at the first error. To check every key a type doesn’t have, set `UnmappedMemberHandling = YamlUnmappedMemberHandling.Disallow` ([parse YAML into classes](https://recursiveai.org/oneyaml/csharp/cookbook/parse-yaml-into-classes/)).