Sunlight is a production-grade, static Certificate Transparency (CT) log implementation written in Go, sponsored by Let's Encrypt. It implements the C2SP Static CT API and provides both a write-path log server (cmd/sunlight) and a read-path static file server (cmd/skylight). The system accepts certificate submissions via the RFC 6962 add-chain/pre-chain endpoints, sequences them into a Merkle tree using the tlog library, and publishes tiles (hash, data, names) along with signed checkpoints. It also supports the tlog-witness and tlog-mirror protocols for transparency and cross-checking. The architecture is modular: the core log engine lives in internal/ctlog with pluggable backends for storage (local filesystem, S3, in-memory) and distributed locking (SQLite, DynamoDB, ETag-based S3). The sequencer uses a pool of pending entries with low-priority eviction, batched sequencing, and staged uploads via tarballs for crash recovery. Deduplication is handled via a SQLite cache with 256-bit hashes. The system includes extensive observability with Prometheus metrics, structured logging, and debug endpoints for heavy hitters and SSL key logging. Key entry points include the main server binaries (cmd/sunlight, cmd/skylight), a key generation tool (cmd/sunlight-keygen), a partial tile garbage collector (cmd/partial-aftersun), a cache recomputation tool (cmd/recompute-cache), and a names tile generator (cmd/names-prism). The client library (client.go) provides a high-level API for fetching and verifying log entries and inclusion proofs. External dependencies include certificate-transparency-go, torchwood, and golang.org/x/mod/sumdb/tlog. The codebase demonstrates high craftsmanship with several reusable internal packages: durable crash-safe file writes, immutable file flag setting, HyperLogLog cardinality estimation, Space Saving heavy hitters, and a custom XAES-256-GCM implementation. Testing is extensive, including in-memory fake backends, synctest for time-dependent rate limits, and deterministic test data generation.