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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses the caching window, upstream data source, the fact that it is fetched live rather than stored, and the billing behavior including that failed calls are not charged. For a paid, externally sourced call that is exactly the operational context an agent needs before invoking.

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?

Effectively structured: what it returns first, then freshness, then the negative disambiguation, then cost. Every sentence carries information, though the payment-rail enumeration (Base, Solana, Arc) is slightly more detail than an agent needs to select the tool.

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?

Complete for a zero-parameter read tool: source, fields, refresh rate, cache TTL, cost model, and failure semantics are all stated, and a return-value contract is covered by the output schema. Nothing an agent needs in order 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?

There are zero parameters, so the baseline is 4 by rule. The description correctly implies a parameterless 'give me the current value' call and adds no misleading parameter expectations.

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 resource and scope: live ISS position with the exact fields returned (latitude, longitude, altitude, speed, daylight status), and names the upstream source. The explicit 'Not a real-estate dataset' line preempts the misleading 'realestate_' name prefix, which is the key disambiguation an agent needs here.

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?

Usage is clear from the framing (fetch current ISS position) and the freshness contract ('updates roughly every second; cached 30 seconds') tells the agent when a repeat call adds no new information. It lacks an explicit 'do not use for X, use Y instead' clause, but no sibling covers this data, so the omission is minor.

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