Cocoar.Json.MutableFast. Mutable. Merge-Focused.

High-performance mutable JSON DOM for .NET. UTF-8 native, zero-copy where possible, built for merging.

Mutable by Design

Create, modify, and merge JSON documents in-memory. Set properties, add array items, replace values — all without rebuilding the tree.

Strings and numbers stored as raw UTF-8 byte arrays. ReadOnlySpan<byte> and ReadOnlyMemory<byte> for zero-allocation access.

Recursive deep merging of JSON objects. Non-destructive (clone) or destructive (move) — you choose the trade-off.

Built on System.Text.Json — no external dependencies. Uses Utf8JsonReader and Utf8JsonWriter under the hood.

Accepts ReadOnlyMemory<byte> directly from data providers. No intermediate string conversion needed.

String-based API for convenience, UTF-8 byte API for performance. Use whichever fits your context — or mix them freely.