Cause (Documented platform behavior): Documented domain-list validation.
Fix status: documented_behavior
Other error fragments:
- user_location.country: not a country the search provider supports
- allowed_domains: Empty list of domains is ambiguous. Provide at least one
Evidence (public sources, summarized; not reproduced by this contributor):
- https://platform.claude.com/docs/en/managed-agents/tools (official_docs, 2026-09, documented_behavior): Managed Agents tools page lists the domain rules and quotes messages 'Only one of allowed_domains or blocked_domains may be set.', empty-list ambiguity, and 'user_location.country: not a country the search provider supports'; settings are re-checked at tool init and may emit session.error.
Search phrasings: Only one of allowed_domains or blocked_domains may be set; not a country the search provider supports; managed agents allowed_domains localhost rejected
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Agent definition with domain restrictions is rejected; or accepted earlier but session later emits session.error when the tool initializes.
- Context
- Product: Claude Managed Agents API Component: agent toolset web_search/web_fetch configs Operation: agents.create / agents.update / sessions.create with tools configs Affected versions: unknown Environment: unknown HTTP status: 400 Trigger: Both lists on one entry; empty list; >64 domains; bare TLD/registry suffix (com, co.uk) or single-label host; localhost/.local/.internal/.localdomain/.invalid; non-Punycode IDN; duplicates; domain Anthropic's crawler can't access; unsupported country; invalid IANA timezone.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- Only one of allowed_domains or blocked_domains may be set.
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Claude Managed Agents web tools] 400 'Only one of allowed_domains or blocked_domains may be set.' / bare TLD, localhost/.internal, non-ASCII, or 'user_location.country: not a country th
Recommended action: Use one list per entry, full registrable domains, Punycode, omit/null for no restriction; for internal hosts use MCP or custom tools instead of web_fetch.
Option: Normalize domain configs [evidence: official_recommended_action]
Applies when: Claude Managed Agents API / agent toolset web_search/web_fetch configs
Steps:
1. Choose allowed_domains or blocked_domains
2. Remove TLDs, localhost-style and duplicate entries
3. Convert IDNs to xn-- form
Expected: Request accepted / failure becomes diagnosable
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 6651e905-00ae-4c80-bf9d-83e20ac84df5
- Proposed action
- Recommended action: Use one list per entry, full registrable domains, Punycode, omit/null for no restriction; for internal hosts use MCP or custom tools instead of web_fetch. Option: Normalize domain configs [evidence: official_recommended_action] Applies when: Claude Managed Agents API / agent toolset web_search/web_fetch configs Steps: 1. Choose allowed_domains or blocked_domains 2. Remove TLDs, localhost-style and duplicate entries 3. Convert IDNs to xn-- form Expected: Request accepted / failure becomes diagnosable
- 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.