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

Annotations only cover the read-only safety profile; the description adds substantial behavior beyond that: the ~50-brand coverage, the cheapest-first ordering, the one-row-per-brand selection rule, price freshness (date read), app/account requirements, and a source link. The disclosure that Inbox eSIM's own row is flagged is_ours yet keeps its true price position is exactly the kind of commercial-bias context an agent cannot infer from structured fields.

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 core purpose and ordering are front-loaded in the first clause, and the remaining sentences each carry real information about output fields and the is_ours caveat. The final sentence is dense and could be split or trimmed, but nothing is filler.

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 four-parameter comparison tool with a fully documented schema and an output schema, the description covers selection logic, ordering, freshness, and the vendor-bias caveat. An agent has everything needed to call it and to interpret the result correctly.

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%, so destination, data_gb, min_days, and unlimited are already documented with defaults. The description adds only that the request is a "size" and a "trip length" and that plans must "cover" the request, which largely restates the schema's "at least this much data" and "valid for at least this many days" wording.

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 ("Compares travel eSIM prices") plus scope (one country, ~50 brands, cheapest first, constrained by size and trip length). That is clearly distinguishable from siblings like find_esim_plans or buy_esim without opening any 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?

The description makes clear this is the cross-brand price-comparison path and implies a single-country request, which routes the agent away from find_esim_plans and buy_esim. It never names an alternative tool or states an explicit exclusion, so the when-not guidance is left implicit.

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