# Programmatic API

## Core Function

```python
import onnx_doctor

messages = onnx_doctor.diagnose(model, providers)
```

The `diagnose` function walks the IR tree and dispatches to each provider's
check methods (`check_model`, `check_graph`, `check_node`, etc.).

## DiagnosticsMessage

Each message contains:

- `error_code`: The rule code (e.g. `ONNX001`).
- `severity`: `error`, `warning`, or `info`.
- `message`: Human-readable description.
- `target_type`: What kind of IR object (`model`, `graph`, `node`, etc.).
- `target`: The actual IR object reference.
- `rule`: The `Rule` object (if available), with `explanation`, `suggestion`, etc.
- `suggestion`: Per-instance fix suggestion.
- `location`: Human-readable location string.

## Rule

```python
from onnx_doctor import Rule

rule = Rule(
    code="CUSTOM001",
    name="my-custom-rule",
    message="Something is wrong.",
    default_severity="warning",
    category="spec",
    target_type="node",
    explanation="Detailed explanation...",
    suggestion="How to fix it.",
)
```

## RuleRegistry

```python
from onnx_doctor import RuleRegistry
from onnx_doctor._loader import get_default_registry

# Get all built-in rules
registry = get_default_registry()
rule = registry.get("ONNX001")
rule = registry.get("empty-graph-name")  # Also works by name
```