---
title: json_schema
sidebarTitle: json_schema
---

# `fastmcp.utilities.json_schema`

## Functions

### `resolve_root_ref` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/json_schema.py#L7" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
resolve_root_ref(schema: dict[str, Any]) -> dict[str, Any]
```


Resolve $ref at root level to meet MCP spec requirements.

MCP specification requires outputSchema to have "type": "object" at the root level.
When Pydantic generates schemas for self-referential models, it uses $ref at the
root level pointing to $defs. This function resolves such references by inlining
the referenced definition while preserving $defs for nested references.

**Args:**
- `schema`: JSON schema dict that may have $ref at root level

**Returns:**
- A new schema dict with root-level $ref resolved, or the original schema
- if no resolution is needed


### `compress_schema` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/json_schema.py#L240" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
compress_schema(schema: dict, prune_params: list[str] | None = None, prune_defs: bool = True, prune_additional_properties: bool = True, prune_titles: bool = False) -> dict
```


Remove the given parameters from the schema.

**Args:**
- `schema`: The schema to compress
- `prune_params`: List of parameter names to remove from properties
- `prune_defs`: Whether to remove unused definitions
- `prune_additional_properties`: Whether to remove additionalProperties\: false
- `prune_titles`: Whether to remove title fields from the schema