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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful context beyond that: no sign-up is required, the downstream flow is order → pay → QR code, and each plan carries an order_url. It omits pagination/rate-limit behavior, keeping it short of a 5.

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 key facts (plans, cheapest first, no sign-up, currency rule) are front-loaded and the whole thing is a few tight sentences. There is minor duplication of the schema's currency text, which costs it a point.

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 should carry more of the return shape; it only mentions prices and order_url per plan and says nothing about data volume, validity period, or coverage per plan. It is adequate to make the call, but an agent cannot anticipate the result structure.

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 both parameters are already documented. The description's notes on location formats and on USD-outside-Nigeria / NGN-in-Nigeria largely restate the schema's own currency description, adding reinforcement rather than new meaning, so the baseline of 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?

The description states a specific resource (eSIM data plans), a scope (one destination) and an ordering rule (cheapest first, with prices). It implicitly distinguishes itself from siblings like list_esim_locations (locations, not plans) and create_esim_order (ordering, not searching), though it never names them 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?

It tells the agent what input to supply (a country or region name or code, with examples), which implies the usage context. But it never says when to prefer this tool over list_esim_locations or search_phone_plans, nor any when-not conditions or prerequisites.

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