# The .slm Model Format

> .slm is the project-specific binary model artifact designed for strict browser loading, bounded validation, and compact local execution.

- Site: TinyRustLM
- Canonical: https://TinyRustLM.mirust.com/slm-format/
- Version: 1.3.0
- Updated UTC: 2026-06-29T22:59:10Z

## Why not generic model files

Generic model formats are flexible, but that flexibility usually requires broader parsers, larger metadata surfaces, and more runtime interpretation. TinyRustLM uses a narrower artifact contract so the browser runtime can validate and load only what it knows how to execute.

- Header validation
- Tensor directory validation
- Tokenizer checksum
- Layout checksum
- Finite payload checks

## Structural invariants

The format records explicit model dimensions and tensor entries. Header fields must be non-zero, tensor entries must point inside the file, declared shapes must match payload counts, and checksums must bind the artifact before generation is allowed.

- 108-byte header target
- 64-byte tensor entries
- Non-zero checksum
- No NaN or Infinity payloads

## Tokenizer inclusion

The runtime supports byte-level fallback and compiled BPE metadata. Tokenizer data belongs inside the model artifact or its verified sidecar path so generation does not depend on Python-only tokenizer files at runtime.

- Byte fallback
- BPE metadata
- Bounded decode
- Tokenizer drift checks