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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description adds behavior beyond that: results are capped at three fits, each carries full plan facts plus a total trip price, and the reason is constrained to catalogue facts only. It does not mention auth needs, rate limits, or fallback behavior when nothing fits.

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?

Two tightly packed sentences, front-loaded with the purpose and output shape before the routing instruction. Little waste, though the middle clause is dense enough that it could be split for scannability.

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 an 8-parameter read tool with an output schema, the description covers purpose, output shape, and routing, so return-format gaps are excused by the output schema. Missing only explicit sibling naming and edge-case behavior, which are minor given the structured coverage.

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 8 parameters in detail. The description only restates countries (1-5, any language), days, and data usage, adding no format or constraint detail beyond the schema. 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?

States a specific verb+resource ('Turn a trip into up to three plan recommendations') and enumerates the core inputs (countries, days, data usage). It also implicitly distinguishes itself from the list-oriented sibling by framing itself as the trip-description entry point rather than a list search.

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?

Explicitly says 'Use this first whenever the user describes a trip rather than asks for a list,' giving both a when-to-use and a contrasting condition that routes to a list-style sibling. It stops short of naming that sibling (search_esim_plans) or stating exclusions, so it is clear but not fully prescriptive.

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