simdjson is a high-performance C++ JSON parsing library that uses SIMD instructions (AVX2, AVX-512, NEON, RVV, etc.) to parse and validate JSON at multi-gigabyte-per-second speeds. It provides two primary APIs: a DOM API (`simdjson::dom`) that builds a complete in-memory tree, and an On-Demand API (`simdjson::ondemand`) that performs lazy, forward-only parsing for streaming and large-document use cases. The library also includes a builder API for JSON serialization, compile-time JSON parsing via C++26 reflection, JSON Pointer/Path support, NDJSON/JSON-sequence streaming, and a single-header amalgamated distribution. The codebase is organized around a two-stage pipeline: stage 1 performs SIMD-accelerated structural indexing and UTF-8 validation, and stage 2 builds the DOM tape or drives the on-demand iterator. Runtime CPU dispatch selects the best implementation for the host architecture, with fallbacks for non-SIMD platforms. The repository is a mature, production-grade library used by major projects (Node.js, ClickHouse, etc.) and is backed by an extensive test suite, fuzzing harnesses, and cross-architecture CI. It is primarily an application/library rather than a data-research repository, though it contains benchmark and research-oriented components (e.g., performance modeling, static reflection experiments).