Reading and writing

Read an archive

HarDocument reads JSON from three sources:

Property names are matched case-insensitively. Invalid JSON throws a JsonException, and a document that is the JSON null throws an InvalidOperationException. A stream is not closed.

Create and write an archive

Build the model with object initializers, then write it with WriteTo or WriteToAsync, to any stream:

var document = new HarDocument
{
    Log = new HarLog
    {
        Version = "1.2",
        Creator = new HarCreator
        {
            Name = "MyTool",
            Version = "1.0.0",
        },
        Entries =
        [
            new HarEntry
            {
                StartedDateTime = DateTimeOffset.UtcNow,
                Request = new HarRequest
                {
                    Method = "GET",
                    Url = "https://example.com/api/data",
                },
                Response = new HarResponse
                {
                    Status = 200,
                    StatusText = "OK",
                },
            },
        ],
    },
};

using var stream = new MemoryStream();
await document.WriteToAsync(stream, indented: true);

To write to a file, pass the FileStream returned by File.Create("output.har"). ToJsonString returns the JSON as a string:

var document = new HarDocument();
document.Log!.Creator = new HarCreator { Name = "MyTool", Version = "1.0" };
document.Log.Entries!.Add(new HarEntry
{
    StartedDateTime = new DateTimeOffset(2026, 1, 15, 10, 0, 0, TimeSpan.Zero),
    Request = new HarRequest { Method = "GET", Url = "https://example.com/" },
    Response = new HarResponse { Status = 204, StatusText = "No Content" },
});

var json = document.ToJsonString(indented: true);

var copy = HarDocument.Parse(json);
Assert.Equal("1.2", copy.Log!.Version);
Assert.Equal(204, Assert.Single(copy.Log.Entries!).Response!.Status);

• indented: true formats the JSON on several lines. The default is compact JSON.
• A new HarDocument already has a Log with Version 1.2, a Creator and an empty Entries list, so you can add entries to it.
• A new HarEntry has empty Request, Response, Cache and Timings objects; set the values you know.
• A property whose value is null is not written.

Custom fields

Tools add their own fields to the objects of the format, with names that start with _. The fields the model does not define are kept in the ExtensionData dictionary of each object, and written back:

var document = HarDocument.Parse("""
    {
      "log": {
        "version": "1.2",
        "entries": [
          { "_resourceType": "xhr", "request": { "method": "GET", "url": "https://example.com/" } }
        ]
      }
    }
    """);

var entry = Assert.Single(document.Log!.Entries!);
Assert.Equal("xhr", entry.ExtensionData!["_resourceType"].GetString());

// Custom fields are written back
Assert.Contains("\"_resourceType\":\"xhr\"", document.ToJsonString());

The values are JsonElements. To add a field, add an entry to the dictionary; it is null until the object has a field to hold, so create it first.

Values the format uses for unknown data, such as -1 for a timing that does not apply, are read and written as they are.