# Schema Guard Plugin
> Author: Mihai Criveti
> Version: 0.1.0
Validates tool args and results against a minimal JSONSchema-like subset (type, properties, required).
## Hooks
- tool_pre_invoke
- tool_post_invoke
## Config
```yaml
config:
arg_schemas:
calc:
type: object
required: [a, b]
properties:
a: {type: integer}
b: {type: integer}
result_schemas:
calc:
type: object
required: [result]
properties:
result: {type: number}
block_on_violation: true
```
## Design
- Validates against a small subset of JSONSchema: `type`, `properties`, `required`, and array `items`.
- Pre-hook checks input args; post-hook checks tool result.
- Blocking behavior controlled by `block_on_violation`; otherwise attaches `schema_errors` in metadata.
## Limitations
- No support for advanced JSONSchema keywords (e.g., `oneOf`, `allOf`, `format`, `enum`).
- No automatic coercion; values must already match the schema types.
- Deep/nested validation supported only through nested `properties`/`items` in the provided schema.
## TODOs
- Add optional type coercion (e.g., strings to numbers/booleans).
- Extend keyword support (min/max, pattern, enum, string length).
- Schema registry integration and per-tool versioning.
