What happened?
When hydrating a tool call response.data based on a JSON schema, if the tool call output schema has a boolean value for it's one of it's properties, fastmcp fails parsing. This is a valid scenario (since draft 06: https://json-schema.org/draft-06/draft-wright-json-schema-01#rfc.section.4.4) which is equivalent to the value being {}.
Example Code
from fastmcp.utilities.json_schema_type import json_schema_to_type
schema = {'$schema': 'https://json-schema.org/draft/2020-12/schema', 'title': 'DeduplicatedLogs', 'type': 'object', 'properties': {'timeRange': {'$ref': '#/$defs/FromTo'}, 'totals': {'$ref': '#/$defs/Totals'}, 'entries': {'type': 'array', 'items': {'$ref': '#/$defs/LogWithCount'}}}, 'required': ['timeRange', 'totals', 'entries'], '$defs': {'FromTo': {'type': 'object', 'properties': {'from_ms': {'description': 'Absolute time in milliseconds since the epoch.', 'type': 'integer', 'format': 'int64'}, 'to_ms': {'description': 'Absolute time in milliseconds since the epoch.', 'type': 'integer', 'format': 'int64'}}, 'required': ['from_ms', 'to_ms']}, 'Totals': {'type': 'object', 'properties': {'fetched': {'type': 'integer', 'format': 'uint', 'minimum': 0}, 'unique': {'type': 'integer', 'format': 'uint', 'minimum': 0}}, 'required': ['fetched', 'unique']}, 'LogWithCount': {'type': 'object', 'properties': {'log': {'$ref': '#/$defs/LogEntry'}, 'count': {'type': 'integer', 'format': 'uint64', 'minimum': 0}}, 'required': ['log', 'count']}, 'LogEntry': {'type': 'object', 'properties': {'_ts': {'type': 'integer', 'format': 'int64'}, '_line': {'type': ['string', 'null']}, 'message': {'type': ['string', 'null']}, 'level': True, '_app': True, 'app': True, '_host': True, 'host': True, '_tag': {'type': ['array', 'null'], 'items': {'type': 'string'}}}, 'required': ['_ts'], 'additionalProperties': True}}}
json_schema_to_type(schema)Version Information
FastMCP version: 3.2.0
MCP version: 1.26.0
Python version: 3.12.13
Platform: macOS-15.7.4-arm64-arm-64bit
FastMCP root path: /Users/jon.moses/dev/mezmo/qa-mcp-testing/.venv/lib/python3.12/site-packages
What happened?
When hydrating a tool call
response.databased on a JSON schema, if the tool call output schema has a boolean value for it's one of it's properties, fastmcp fails parsing. This is a valid scenario (since draft 06: https://json-schema.org/draft-06/draft-wright-json-schema-01#rfc.section.4.4) which is equivalent to the value being{}.Example Code
Version Information