Spacetimedb Serialization

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.

Reference map

Guidance

• Prefer high-level SDK and module APIs unless the user's task is explicitly about serialization, ABI, or custom tooling.
• Keep byte-level examples tied to the reference notation.
• Route normal client/server code back to the relevant SDK, reducer, table, or procedure skill.