What it is
Bogus generates realistic fake data for .NET — names, addresses, emails, dates and text — for tests, seeding and demonstrations.
Define a Faker<T> describing how to populate each property, then generate one or many. Seeding makes output reproducible.
Installation
dotnet add package BogusGetting started
The smallest useful thing you can do with it, and what each part means.
csharp
var faker = new Faker<Book>()
.UseSeed(42) // deterministic across runs
.RuleFor(b => b.Id, f => f.IndexFaker + 1)
.RuleFor(b => b.Title, f => f.Lorem.Sentence(3).TrimEnd('.'))
.RuleFor(b => b.Year, f => f.Random.Int(1950, 2026))
.RuleFor(b => b.Isbn, f => f.Commerce.Ean13())
.RuleFor(b => b.AddedAt, f => f.Date.Past(2))
.RuleFor(b => b.Author, f => new Faker<Author>()
.RuleFor(a => a.Name, x => x.Name.FullName())
.Generate());
var one = faker.Generate();
var many = faker.Generate(1000);Advanced usage
Where the library earns its place over a simpler alternative.
csharp
var faker = new Faker<Order>()
.RuleFor(o => o.Status, f => f.PickRandom<OrderStatus>())
// 5% of orders have no email — exercise the null path.
.RuleFor(o => o.Email, f => f.Random.Bool(0.95f) ? f.Internet.Email() : null)
.RuleFor(o => o.ShippedAt, (f, o) =>
o.Status == OrderStatus.Shipped ? f.Date.Recent(10) : null)
.FinishWith((f, o) => logger.LogDebug("generated {Id}", o.Id));
// Locale-specific data for internationalisation testing.
var japanese = new Faker<Customer>("ja")
.RuleFor(c => c.Name, f => f.Name.FullName());Errors and fixes
The failures you are most likely to hit, and what actually resolves them.
- Tests fail intermittently
- Unseeded randomness. Call UseSeed, and log the seed if you randomise it deliberately.
- Generated data violates a database constraint
- Bogus does not know your constraints. Add rules matching them, for example unique emails via f.IndexFaker.
Best practices
- Always UseSeed in tests so failures are reproducible.
- Generate some invalid and missing values on purpose; perfect data tests nothing.
- Keep generators next to the tests that use them rather than in one shared file.
- Use locale-specific fakers when testing internationalisation and field lengths.
Background
Why it exists, and what it was reacting to.
A port of JavaScript's faker.js, Bogus replaced the "test1, test2" placeholder data that makes demos look unfinished and hides bugs that only appear with realistic input.