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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new information the annotations cannot carry: no API key or auth is required, the call is free, and it names the actual return payload (including the source URL and verification date, which signals data provenance). It does not cover error behavior for an invalid country slug.

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?

Three short sentences, front-loaded with cost and the core verb, then the empty-argument case, then the auth note. Every sentence carries a distinct fact — pricing, payload contents, listing behavior, auth — with no filler or repetition of the title.

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?

With no output schema, the description correctly compensates by enumerating the returned fields, so an agent knows what it will receive without a trial call. The only remaining gap is failure behavior for a mistyped or unsupported country slug, which matters given the slug list is open-ended in the schema text.

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 both parameters are already documented, and the enum constrains locale. The description's "call without a country" guidance duplicates what the schema already says ("Omit to list all supported countries") and says nothing about the locale parameter or accepted slug format beyond what the schema shows. Baseline 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?

States a specific verb and resource ("Returns the official passport or ID photo requirements for a country") and enumerates exactly what comes back: printed size, head height, background, digital file rules, editing policy, source URL, verification date. This is unmistakably distinct from the siblings get_pricing and remove_background, which an agent can rule out without opening either schema.

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?

"Call without a country to list the countries covered" gives an explicit calling convention for the zero-argument case, which is the main ambiguity for a tool with zero required parameters. It also sets cost expectations up front ("Free", "No API key needed"). It stops short of stating what happens with an unsupported slug or when to prefer another tool, but the sibling set is unrelated so no routing guidance is really needed.

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