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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and scope profile is covered. The description adds the key behavioral fact that results are ids for later fetching, but says nothing about result limits, ranking, empty-result behavior, or matching semantics (partial vs exact).

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 short sentences, zero filler, with the scope ('eSIM destinations by name') front-loaded and the return/chaining note second. Nothing wastes the agent's attention.

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 lookup with a fully documented schema, this covers what is searched and what comes back to enable the next call. The remaining gap is sibling disambiguation from search_esim_plans, which is not addressed.

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 coverage is 100% and the single 'query' parameter already includes an example ('japan esim'). The description adds no syntax, format, or matching guidance beyond the schema, so 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 ('Search what Xpress sells: eSIM destinations by name'), which distinguishes a destination lookup from the plan-search siblings. It's clear what is searched, though the bare name 'search' means the description is doing the differentiation work rather than naming an alternative explicitly.

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 phrase 'Returns ids to pass to fetch' gives useful workflow chaining guidance, implying search-then-fetch. However, there's no explicit statement about when to use this versus search_esim_plans, nor any exclusions or preconditions — usage is implied rather than directed.

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