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

Beyond the readOnly/non-destructive annotations, it discloses that no credits are deducted, that guests can call it without Authorization, and that sandbox keys (test_*) route to the sandbox catalog. These are non-obvious behavioral traits an agent could not 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?

Front-loads the alias relationship and preconditions in short, purposeful sentences. Slightly dense with parentheticals, but every sentence carries information; no 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?

Auth, cost, and sandbox behavior are covered well, and an output schema exists so return values need not be restated. However, with 0% schema description coverage, the description leaves all four input parameters unexplained, which is a material gap for correct invocation.

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 0% and the description explains none of the four parameters (catalog_id, price_token, lang, currency). The mention of return fields (data_gb, checkout_mode, unlimited) does not inform input semantics, leaving required catalog_id/price_token meaning undocumented.

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 ('Preview a travel eSIM order without placing it') and explicitly frames itself as an alias of preview_order scoped to type=esim. An agent can distinguish it from preview_order and from the mutation sibling create_esim_order 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?

Gives clear usage context: callable by guests without Authorization, no credits deducted, and the 'kept for existing connectors' note implies new callers should prefer preview_order with type=esim. It stops short of an explicit when-not/alternative statement, so not a 5.

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