Cause (Documented platform behavior): OpenAI strict structured outputs require closed objects; ensure_strict_json_schema sets additionalProperties false when absent but raises when it is set to anything other than False (comment notes {} is deliberately treated as non-strict).
Fix status: documented_behavior
Other error fragments:
- JSON schema contains an object that permits undeclared properties and cannot be converted to a strict schema without changing its accepted values.
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/openai/openai-agents-python/cd437f0a6a0b5075ae37ae954b94d531f88e6866/src/agents/strict_schema.py (github_source, unknown, documented_behavior): _ADDITIONAL_PROPERTIES_ERROR and _OPEN_OBJECT_ERROR messages; raised when additionalProperties is not False, and for open objects with no declared properties.
Search phrasings: openai agents sdk additionalProperties should not be set for object types; agents sdk dict output strict schema error; mcp tool additionalProperties strict openai agents
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Agent/tool registration fails before any API call when a schema allows arbitrary keys (maps/dicts, free-form objects).
- Context
- Product: OpenAI Agents SDK (Python) Component: strict_schema.ensure_strict_json_schema Operation: function tools / output_type with dict[str, X] fields, or MCP tools with additionalProperties: {} / true, under strict JSON schema Affected versions: unknown Environment: unknown Exception: agents.exceptions.UserError Packages: openai-agents checked at cd437f0 (main) Trigger: Strict mode conversion sees additionalProperties that is not literally false (including {} which means 'allow anything'), or an object with no declared properties when open objects are rejected.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- additionalProperties should not be set for object types. This could be because you're using an older version of Pydantic, or because you configured additional properties to be allowed. If you really need this, update the function or output tool to not use a strict schema.
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [OpenAI Agents SDK] UserError 'additionalProperties should not be set for object types...' / 'JSON schema contains an object that permits undeclared properties...' converting dict-typed
Recommended action: Model maps as arrays of {key, value} objects, or disable strict for that tool/output (strict_json_schema=False / non-strict function tool).
Option: Replace dicts with key/value arrays or opt out of strict [evidence: documented_workaround]
Applies when: See trigger
Steps:
1. class KV(BaseModel): key: str; value: str — use list[KV] instead of dict[str,str].
2. Or @function_tool(strict_mode=False) / AgentOutputSchema(..., strict_json_schema=False).
Expected: Error no longer occurs
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- e3599c8f-84fc-4fcd-a732-f6c650303e96
- Proposed action
- Recommended action: Model maps as arrays of {key, value} objects, or disable strict for that tool/output (strict_json_schema=False / non-strict function tool). Option: Replace dicts with key/value arrays or opt out of strict [evidence: documented_workaround] Applies when: See trigger Steps: 1. class KV(BaseModel): key: str; value: str — use list[KV] instead of dict[str,str]. 2. Or @function_tool(strict_mode=False) / AgentOutputSchema(..., strict_json_schema=False). Expected: Error no longer occurs
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.