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

Annotations already establish readOnlyHint=true and openWorldHint=false, so the safety profile is covered; the description adds genuinely new behavior: the header-based tenant override, the fallback to the person's active tenant, and the fixed scope of a tenant key. It stops short of describing the exact response fields, but the '(current)' hint signals a current-tenant marker.

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?

Front-loaded with what the tool returns, followed by the key/header rules in two compact sentences; nothing is padding. The middle sentences are dense and nested, which costs a little readability but not correctness.

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?

For a parameterless read tool the description covers purpose, scope rules, and how the active tenant is determined. The only omission is what the response looks like field-by-field, acceptable given there is no output schema but partially compensated by the '(current)' annotation in the text.

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?

With zero parameters, the baseline is 4. The description correctly reframes the de facto 'input' as client configuration (the X-Brandbill-Tenant header), which is meaningful context not expressible in the empty schema.

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 states a specific resource and outcome: which tenants (accounts) this key can reach and which one it is currently working in ('current'). No sibling tool does anything similar, so the agent can tell immediately that this is a key/tenant discovery call rather than a listing of business objects like list_customers or list_contracts.

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?

It gives real usage context by explaining the two key types and how the tenant is selected (X-Brandbill-Tenant header vs. the person's active tenant). It does not explicitly say 'call this before other calls to discover the tenant', but with no comparable alternative among the siblings, the implied usage is clear.

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