Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context by listing the possible status values and the special 'current' behavior when app_id is supplied. It explains what the call returns at a high level, which is sufficient for a read-only check.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences with no filler. The primary purpose and usage context come first, followed by the return semantics and the app_id nuance. Every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The description is complete enough for a simple read-only check: it states what is checked, what is returned, and the optional parameter's effect. No output schema exists, so the return-value summary is especially valuable. A small gap is that it does not elaborate on what 'empty' means, but that is minor given the tool's simplicity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents both parameters adequately. The description reinforces subdomain's role and explains app_id's effect, but it does not add material meaning beyond what the schema already states. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource: 'Check whether a platform subdomain can be claimed before calling set_app_subdomain.' It clearly distinguishes this from sibling tools like check_domain_verification by focusing on subdomain claimability rather than domain verification. It also specifies the relationship to set_app_subdomain, making the tool's role unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use the tool: before calling set_app_subdomain. It also explains the conditional use of app_id and how it changes the reported status. It falls just short of a 5 because it does not explicitly mention when not to use it or name alternative tools for domain checks, though the context is sufficient.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.