Use this skill for low-level encoding, wire formats, and module ABI work.

Core encoding facts

Prefer generated SDKs and module APIs unless the task is explicitly custom tooling, protocol inspection, ABI work, or serialization debugging.
BSATN encodes product values as field values in order; field names are not encoded.
BSATN encodes strings as u32 byte length followed by UTF-8 bytes.
BSATN encodes integer and float primitive payloads in little-endian form; floats use their raw IEEE bit representation.
SATS JSON product values can be arrays by field order or objects by field name.
SATS JSON encodes integer types as JSON numbers, so large 64-bit, 128-bit, and 256-bit values can lose precision in normal JavaScript number handling.
Sum values are tagged unions; the tag is the variant index or name depending on the format.

ABI cautions

WebAssembly ABI functions use the C ABI on wasm32 and often communicate through pointer/length pairs.
Most host functions return u16, with 0 meaning success; outputs are written through out pointers.
Some UTF-8 handling is lossy; invalid bytes may be replaced.
Buffer functions have explicit ownership rules. Do not reuse consumed host buffers.