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

With no annotations, the description carries the full burden and does so richly: it discloses the returned artifact (a key with a daily spend cap), that the cap is immutable ('cannot be raised later'), the payment model (Lightning, no free call), and where the free call actually lives. The permanent-constraint disclosure is exactly the kind of behavioral context an agent needs before committing.

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 purpose, then usage condition, then behavior, then the alternative route — good ordering. Slightly redundant ('no human required' restated as 'no signup form, no login'), costing a little tightness against an otherwise dense paragraph.

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 one-optional-param tool with no output schema, the description covers what it returns, the constraints on that return, the cost model, and the fallback path. Nothing needed to call it correctly is missing.

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 coverage is 100% and the single parameter is fully documented, so baseline is 3. The description goes beyond the schema by framing the cap as permanent ('cannot be raised later'), adding decision-relevant meaning the schema fields do not convey.

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?

States a specific verb+resource ('Self-register for an operator API key') and immediately scopes it with 'no human required — no signup form, no login'. An agent knows exactly what this produces and how it differs from a human account signup.

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?

Explicitly states the condition: 'Use this if you don't already have an api_key from a human operator.' It also names the alternative path (human signup at the shop URL) and the trade-off (higher cap, ongoing monitoring), so selection is unambiguous.

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