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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds one genuinely useful behavioral fact not in structured data: the required 'X-Agent-Key' header. It says nothing about rate limits, scope of the agent identity, or freshness of the usage data.

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 short fragments with no padding, and the resource is front-loaded before the auth requirement. The telegraphic style is efficient, though the fragment form reads more like a note than a specification.

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 zero-parameter, read-only tool with no output schema, the description supplies both the return content (tier, limits, usage today) and the auth prerequisite, which is most of what an agent needs. It stops short of clarifying the 'me' vs 'get_agent' boundary.

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?

The tool takes zero parameters, so the baseline of 4 applies. The description correctly avoids inventing parameter details and simply indicates the invoking agent is the implicit subject.

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 the resource ('Your agent') and the fields returned (tier, limits, usage today), so the content is inferable. However, there is no verb and no differentiation from the sibling 'get_agent', which an agent could easily mistake for the same operation. The purpose is gestured at rather than stated.

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?

There is no explicit when-to-use guidance, no conditions, and no exclusions. The presence of a sibling named 'get_agent' makes this a real ambiguity the description never resolves, leaving the agent to guess which of the two to call.

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