Libreyolo API Conventions

LibreYOLO API conventions

AGENTS.md's general constraint: every user-facing API (Python, CLI, YAMLs) follows the de-facto YOLO ecosystem standard, so users' existing scripts, datasets, and muscle memory transfer. REVIEW.md enforces it as an axiom. This skill is what that means concretely, plus how to check parity without license risk.

The parity-check method (license-critical)

The dominant YOLO library is AGPL. To keep LibreYOLO clean:

• Never read its source code to answer "how does the standard behave?". Exposure creates contamination risk (see libreyolo-license-audit).
• Do read its public documentation (docs pages, API reference) to learn the behavioral contract: argument names, return shapes, attribute names. Facts about an interface, learned from docs, are safe; code is not.
• Verify current LibreYOLO behavior by running LibreYOLO, not from memory.
• Where LibreYOLO deliberately deviates, the deviation must be documented where users hit it (docstring + docs page), not discovered.

This doc-only method is established practice here (it is how classify predict/val parity was specified) and is not yours to relax.

The core contracts

CLI and Python mirror each other. Same verbs (predict, train, val, export, track), same argument names, same defaults. A capability added to one side lands on both sides in the same PR, or the PR says why not.

CLI argument grammar: both YOLO-style key=value and --key value are accepted (libreyolo/cli/parsing.py). Every command supports --json (machine-readable stdout), --quiet, and --help-json (full argument schema). New flags must work in both grammars and appear in --help-json automatically by being declared properly, never hand-parsed from argv.

predict returns: a single Results for a single image; a list[Results] for multi-input (directory, list, batched); a generator with stream=True. Do not change this shape per family or per task; downstream code indexes on it. (Indexing a single Results selects a detection, which is exactly why the shape must stay predictable.)

Results stays flat. New task outputs are new flat attributes (r.boxes, r.masks, r.keypoints, r.probs, r.obb, r.gaze, r.semantic_mask, r.depth_map, r.restored, r.points), each a payload class with data on the original image canvas. Never nest, never return raw tensors in model-input coordinates.

val returns a metrics object whose attribute names are the ecosystem's (.top1/.top5 for classify, mAP-family keys for detection). Metric keys are public API: renaming one requires a deprecated alias and a loud changelog entry ("Changed output semantics" is its own changelog section in skills/libreyolo-release for this reason).

Explicit user kwargs beat defaults (REVIEW.md axiom), and CLI defaults are family-derived: the family declares its input size / thresholds, the CLI reads them from the loaded model rather than hardcoding. The worst violation class is accept-and-ignore: an argument that parses successfully but does nothing must instead either work or raise (distill_model's reserved-arg NotImplementedError guard is the sanctioned pattern for not-yet-implemented surface).

Dataset YAMLs and label formats follow the ecosystem format (a competitor-exported dataset must load unchanged); extensions (e.g. masks_dir, input_dir/target_dir) are additive keys documented in docs/dataset_schema.md.

Weights resolution: a bare canonical filename (LibreYOLO9t.pt) auto-downloads; a path is a path; extra-dependent families fail with the exact pip install libreyolo[<extra>] line in the error.

Known sanctioned deviations

Deviations exist where honesty beats imitation; they are documented, not accidental. The load-bearing example: RF-DETR's train signature keeps its recipe's native argument names (batch_size, absolute lr, output_dir) because mapping YOLO-style knobs onto a DETR recipe would accept-and-ignore or silently reinterpret them, which is worse than a visible difference. REVIEW.md pins this ("RF-DETR ignores generic YOLO augmentation knobs", "RF-DETR learning rate is absolute"). Match this pattern: deviate loudly and document, or conform exactly; nothing in between.

Naming rules (from docs/nomenclature.md, the contract file)

• Model classes: Libre<FAMILY> exported from libreyolo/__init__.py.
• Weight files: Libre<FAMILY><size>[-<task>][-<variant>].pt, sizes lowercase, detect suffixless, task suffixes from libreyolo/tasks.py.
• Task aliases: generous on input (seg, segmentation resolve), exactly one canonical name in filenames and metadata.
• New user-visible names (CLI commands, kwargs, metric keys, YAML keys) get checked against the ecosystem's documented name first; invent only when the ecosystem has no name for it.

Review checklist for any new public surface

1. Name exists in the ecosystem standard? Use it verbatim (from docs).
2. Both CLI grammars, --json, --quiet, --help-json covered?
3. Python and CLI land together?
4. Return shape consistent with the contracts above?
5. Any accepted-but-ignored input? (Blocking.)
6. Docstring + docs page + docs/nomenclature.md/dataset_schema.md updated if a contract file is affected?
7. Unit tests assert the shape/name, so parity cannot silently regress.

Related

• docs/nomenclature.md, docs/dataset_schema.md: the contract files.
• skills/libreyolo-add-cli-command/: implementing the CLI side.
• skills/libreyolo-add-task/: contracts for new output kinds.
• skills/libreyolo-license-audit/: why the docs-only rule is absolute.