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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: the call is paid (0.01 USDC per call), the price is only meaningful while the provider still offers the type, and AWS series older than ~10 days are likely retired while GCP/Azure reprice rarely. This goes beyond the annotations and helps the agent interpret results correctly. A small gap: it doesn't describe the exact response shape, but with no output schema and read-only annotations, the added context is strong.

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?

The description is compact and front-loaded: it starts with the paid nature and the core purpose, then adds timestamp interpretation context, and ends with the sibling alternative. Every sentence earns its place, and the structure is easy to scan.

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 read-only, idempotent, single-instance lookup tool with 100% schema coverage, the description is nearly complete. It covers cost, data meaning, timestamp interpretation, and the alternative for broader queries. The only missing piece is the exact response format, but since there is no output schema and the tool is simple, this is a minor gap. The description is complete enough for an agent to select and invoke the tool correctly.

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 description coverage is 100%, so the schema already documents all three parameters (provider, region, instance) with examples and enum values. The description adds the notion that the price is per zone and product, which implies the instance parameter is a type name, but it doesn't add much beyond the schema. Baseline 3 is appropriate because the schema does the heavy lifting.

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 verb ('spot_latest' returns the most recent price event per zone and product for one instance type), names the resource (spot price events), and distinguishes itself from the sibling /spot/snapshot by noting that snapshot returns every type in a region at once. This is a clear, specific purpose that an agent can act on.

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?

The description explicitly says when to use this tool (for the current price in force per zone/product for one instance type) and when not to use it (for every type in a region at once, use /spot/snapshot). It also provides context about AWS vs GCP/Azure timestamp interpretation, which helps an agent decide if the data is meaningful. This is explicit usage guidance with an alternative named.

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