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

With no annotations, the description carries the full behavioral burden but only implies a read operation. It does not state whether the call requires authentication with the same key, whether it consumes quota, what units the balance is in, or what happens for an invalid key.

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?

A single front-loaded sentence with no waste. It is appropriately sized for a one-parameter lookup, though it is so brief that it sacrifices helpful detail for brevity.

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 tool is simple, has one fully documented required parameter, and no output schema, so the description does not need to explain return values. However, for a tool with no annotations it leaves the behavioral profile (auth, side effects, error cases) entirely unspecified.

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?

There is a single parameter with 100% schema description coverage, so the schema already documents 'key' as the API key. The description adds nothing about the parameter and does not need to, so the baseline of 3 applies.

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 the resource ('balance of an API key') but has no verb and does not differentiate from siblings such as create_key or check_domain, which are far apart in function. An agent can infer it is a lookup, but the phrasing is terse and would not distinguish it from a hypothetical sibling that also reports key attributes.

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 when-to-use or when-not-to-use guidance, no mention of prerequisites, and no alternatives named. The agent must infer that this is a plain read of a key's remaining quota.

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