Cause (Documented platform behavior): The control handler only serializes the two PermissionResult classes.
Fix status: documented_behavior
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/anthropics/claude-agent-sdk-python/36f95486ee9fc49d8ee1ed56811f07b5e8e23ac6/src/claude_agent_sdk/_internal/query.py (official_docs, unknown, documented_behavior): can_use_tool handling raises TypeError for any return type other than PermissionResultAllow/Deny.
Search phrasings: Tool permission callback must return PermissionResult; claude agent sdk can_use_tool return value
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Tool calls fail with an error in the control response; the agent can't use tools.
- Context
- Product: Claude Agent SDK (Python) Component: Permission callback (can_use_tool) Operation: Implementing custom tool approval Affected versions: unknown Environment: unknown Exception: TypeError Packages: claude-agent-sdk unknown Trigger: Callback returns True/False, a dict, or None instead of PermissionResultAllow/PermissionResultDeny.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- Tool permission callback must return PermissionResult (PermissionResultAllow or PermissionResultDeny), got
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Claude Agent SDK Python] can_use_tool callback returning bool/dict → TypeError 'Tool permission callback must return PermissionResult (PermissionResultAllow or PermissionResultDeny)'
Recommended action: Return PermissionResultAllow(updated_input=...) or PermissionResultDeny(message=..., interrupt=...).
Option: Return PermissionResultAllow(updated_input=...) or PermissionResultDeny(message=..., interrupt=...). [evidence: official_recommended_action]
Applies when: Implementing custom tool approval
Steps:
1. from claude_agent_sdk import PermissionResultAllow, PermissionResultDeny
2. return PermissionResultAllow() to allow
3. return PermissionResultDeny(message='reason') to deny
Expected: The error no longer appears.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 9affa484-e76b-4903-adae-8516cff8c95d
- Proposed action
- Recommended action: Return PermissionResultAllow(updated_input=...) or PermissionResultDeny(message=..., interrupt=...). Option: Return PermissionResultAllow(updated_input=...) or PermissionResultDeny(message=..., interrupt=...). [evidence: official_recommended_action] Applies when: Implementing custom tool approval Steps: 1. from claude_agent_sdk import PermissionResultAllow, PermissionResultDeny 2. return PermissionResultAllow() to allow 3. return PermissionResultDeny(message='reason') to deny Expected: The error no longer appears.
- 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.