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

Annotations already cover read-only and idempotent behavior, but the description adds genuinely useful context beyond that: results are sorted cheapest-first, the returned fields are enumerated, prices carry a checked date, and the affiliate_link disclosure clarifies that commissions do not affect pricing. This is meaningful transparency, though it omits anything about coverage gaps, rate limits, or empty-result behavior.

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 purpose is front-loaded in the first clause, followed by return fields and then an affiliate disclosure, which is ordered sensibly. It is fairly dense in the middle sentence but every element (sort order, fields, checked date) carries information.

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 usefully enumerates what the response contains (data allowance, validity, price per GB, network, speed policy, source page, buy link), which is exactly what an agent needs. Minor gaps remain around result ordering edge cases and whether the limit applies before or after filtering, but the core picture is 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%, so every parameter is already documented in the schema, and the description adds little per-parameter meaning beyond the general 'filtered to what a trip needs' framing. Baseline 3 is appropriate when 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 opens with a specific verb and resource ('Find the cheapest travel eSIM data plans for a destination') and names the provider pool, so the agent knows exactly what the tool returns. It does not explicitly distinguish itself from compare_esim_providers or esim_price_index, so sibling differentiation is left implicit.

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?

Phrases like 'filtered to what a trip needs' imply the tool is for trip-specific plan selection, and the filter parameters reinforce that. However, the description never states when to prefer this over compare_esim_providers or esim_price_index, nor any exclusions or prerequisites.

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