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

With no annotations, the description carries the full burden, and it does disclose the payload contents (daily cost per tier, currency, language, best months), which is genuinely useful given there is no output schema. It says nothing about rate limits, authorization, or comparison constraints beyond the schema's max/minItems of 2.

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 economical sentence with the core comparison front-loaded and the returned attributes trailing in a compact list. It is a fragment without an explicit verb, but no words are wasted.

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-parameter, read-only comparison tool with no output schema, the description covers both the input shape (two cities) and the salient return fields, which is what an agent needs. Only the absence of routing guidance relative to destination_costs keeps it short of complete.

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% and the schema already states 'Exactly two city names or slugs,' so the parameter is fully documented structurally. The description only echoes 'two cities' without adding format, slug-vs-name preference, or resolution guidance, so baseline 3 is appropriate.

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 (two cities) and the scope of the comparison clearly, and 'side by side' makes the comparative intent unmistakable versus an unrelated sibling like walking_route. It never names destination_costs, so the distinction from the single-destination cost tool is left implicit 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?

Usage is only implied: the side-by-side framing tells an agent this is the tool for a two-city comparison rather than a lookup. There is no explicit when-to-use, when-not-to-use, or routing to destination_costs for single-city queries, so the guidance is minimal but inferable.

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