Repository: jlowin/fastmcp

Issue:
Disable the "title" field in the generated JSON Schema
### Enhancement Description

Is there a way to disable the title field in the generated JSON schema?

My use case is as follow:

```
@app.tool()
async def method(
    field: str = Field(
        description="description"
    )
```

Generated MCP List Tool output looks like this:
```
                            "field": Object {
                                "default": Null,
                                "description": String("description"),
                                "title": String("Field"),                           <------- to remove
                                "type": String("string"),
                            },
```

I tried passing in json_schema_extra into the field but that wasn't working

Note: I would prefer keeping my tool api flat by not introducing a "BaseModel" object as the method input.

### Use Case

_No response_

### Proposed Implementation

```Python

```

Hints from issue comments:
@jlowin: There is no easy way to remove the title universally. Is it preventing something from working?

The generated schema should mirror whatever argument types you define, for example `def my_tool(x: int, y: str)` should not have a BaseModel in it. @erbenmo: > There is no easy way to remove the title universally. Is it preventing something from working?

Ok. This is preventing me from generating complicated MCP models without consuming too much tokens! About 10% tokens are spent on these titles.


> The generated schema should mirror whatever argument types you define, for example def my_tool(x: int, y: str) should not have a BaseModel in it.

Yes, I mentioned BaseModel because I did find a way to make it work for an entire Model (instead of a Field), but I prefer don't prefer that approach because it creates a nested structure which doesn't feel right
@erbenmo: I am using Field though. Should I use annotation instead? Maybe I can try that.@jlowin: @erbenmo we are able to do this after all, see #449. This will be done automatically.@erbenmo: Amazing... Thanks

Solution patch:
diff --git a/src/fastmcp/utilities/json_schema.py b/src/fastmcp/utilities/json_schema.py
index 2957463..87ea4a7 100644
--- a/src/fastmcp/utilities/json_schema.py
+++ b/src/fastmcp/utilities/json_schema.py
@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import copy
-from collections.abc import Mapping, Sequence
 
 
 def _prune_param(schema: dict, param: str) -> dict:
@@ -25,32 +24,55 @@ def _prune_param(schema: dict, param: str) -> dict:
     return schema
 
 
-def _prune_unused_defs(schema: dict) -> dict:
-    """Remove unused definitions from the schema."""
-    # collect all remaining local $ref targets
+def _walk_and_prune(
+    schema: dict,
+    prune_defs: bool = False,
+    prune_titles: bool = False,
+    prune_additional_properties: bool = False,
+) -> dict:
+    """Walk the schema and optionally prune titles, unused definitions, and additionalProperties: false."""
+
+    # Will only be used if prune_defs is True
     used_defs: set[str] = set()
 
-    def walk(node: object) -> None:  # depth-first traversal
-        if isinstance(node, Mapping):
-            ref = node.get("$ref")
-            if isinstance(ref, str) and ref.startswith("#/$defs/"):
-                used_defs.add(ref.split("/")[-1])
+    def walk(node: object) -> None:
+        if isinstance(node, dict):
+            # Process $ref for definition tracking
+            if prune_defs:
+                ref = node.get("$ref")
+                if isinstance(ref, str) and ref.startswith("#/$defs/"):
+                    used_defs.add(ref.split("/")[-1])
+
+            # Remove title if requested
+            if prune_titles and "title" in node:
+                node.pop("title")
+
+            # Remove additionalProperties: false at any level if requested
+            if (
+                prune_additional_properties
+                and node.get("additionalProperties", None) is False
+            ):
+                node.pop("additionalProperties")
+
+            # Walk children
             for v in node.values():
                 walk(v)
-        elif isinstance(node, Sequence) and not isinstance(node, str | bytes):
+
+        elif isinstance(node, list):
             for v in node:
                 walk(v)
 
+    # Traverse the schema once
     walk(schema)
 
-    # remove orphaned definitions
-
-    defs = schema.get("$defs", {})
-    for def_name in list(defs):
-        if def_name not in used_defs:
-            defs.pop(def_name)
-    if not defs:
-        schema.pop("$defs", None)
+    # Remove orphaned definitions if requested
+    if prune_defs:
+        defs = schema.get("$defs", {})
+        for def_name in list(defs):
+            if def_name not in used_defs:
+                defs.pop(def_name)
+        if not defs:
+            schema.pop("$defs", None)
 
     return schema
 
@@ -67,16 +89,32 @@ def compress_schema(
     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
     """
+    # Make a copy so we don't modify the original
     schema = copy.deepcopy(schema)
+
+    # Remove specific parameters if requested
     for param in prune_params or []:
         schema = _prune_param(schema, param=param)
-    if prune_defs:
-        schema = _prune_unused_defs(schema)
-    if prune_additional_properties:
-        schema = _prune_additional_properties(schema)
+
+    # Do a single walk to handle pruning operations
+    if prune_defs or prune_titles or prune_additional_properties:
+        schema = _walk_and_prune(
+            schema,
+            prune_defs=prune_defs,
+            prune_titles=prune_titles,
+            prune_additional_properties=prune_additional_properties,
+        )
+
     return schema


Test patch:
diff --git a/tests/utilities/test_json_schema.py b/tests/utilities/test_json_schema.py
index cc9cc15..a1b5f15 100644
--- a/tests/utilities/test_json_schema.py
+++ b/tests/utilities/test_json_schema.py
@@ -1,11 +1,21 @@
 from fastmcp.utilities.json_schema import (
-    _prune_additional_properties,
     _prune_param,
-    _prune_unused_defs,
+    _walk_and_prune,
     compress_schema,
 )
 
 
+# Create wrappers for backward compatibility with tests
+def _prune_unused_defs(schema):
+    """Wrapper for _walk_and_prune that only prunes definitions."""
+    return _walk_and_prune(schema, prune_defs=True)
+
+
+def _prune_additional_properties(schema):
+    """Wrapper for _walk_and_prune that only prunes additionalProperties: false."""
+    return _walk_and_prune(schema, prune_additional_properties=True)
+
+
 class TestPruneParam:
     """Tests for the _prune_param function."""
 
@@ -244,3 +254,51 @@ class TestCompressSchema:
         assert "$defs" not in result  # Both defs should be gone
         # Check that additionalProperties was removed
         assert "additionalProperties" not in result
+
+    def test_prune_titles(self):
+        """Test pruning title fields."""
+        schema = {
+            "title": "Root Schema",
+            "type": "object",
+            "properties": {
+                "foo": {"title": "Foo Property", "type": "string"},
+                "bar": {
+                    "title": "Bar Property",
+                    "type": "object",
+                    "properties": {
+                        "nested": {"title": "Nested Property", "type": "string"}
+                    },
+                },
+            },
+        }
+        result = compress_schema(schema, prune_titles=True)
+        assert "title" not in result
+        assert "title" not in result["properties"]["foo"]
+        assert "title" not in result["properties"]["bar"]
+        assert "title" not in result["properties"]["bar"]["properties"]["nested"]
+
+    def test_prune_nested_additional_properties(self):
+        """Test pruning additionalProperties: false at all levels."""
+        schema = {
+            "type": "object",
+            "additionalProperties": False,
+            "properties": {
+                "foo": {
+                    "type": "object",
+                    "additionalProperties": False,
+                    "properties": {
+                        "nested": {
+                            "type": "object",
+                            "additionalProperties": False,
+                        }
+                    },
+                },
+            },
+        }
+        result = compress_schema(schema)
+        assert "additionalProperties" not in result
+        assert "additionalProperties" not in result["properties"]["foo"]
+        assert (
+            "additionalProperties"
+            not in result["properties"]["foo"]["properties"]["nested"]
+        )