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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered; the description earns full credit by adding what annotations cannot: an account-connection prerequisite and the explicit exclusion 'Never returns installation codes', which stops the agent from promising an install code from this call. It also discloses that results are accompanied by off-site simvito.com management links (install, add data), which is real behavioral context for a read tool.

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 sentences, no filler: sentence one front-loads the resource and its returned fields, sentence two carries the two constraints (account required, no installation codes). The parenthetical '(install, add data)' is short and disambiguates what the manage link is for rather than padding.

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 an output schema present, the enumerated return fields are technically redundant, but they orient the agent about what can be promised to a user; annotations cover the safety profile and the auth prerequisite is stated. The only minor gap is behavior in the failure/empty case (no connected account, zero eSIMs), which is left unstated but is readily inferable from 'Requires connecting a Simvito account'.

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?

There is a single optional parameter (locale) and schema description coverage is 100%, with the enum listing all supported language codes and the schema text explaining that names and links follow the locale. The description adds no parameter-level meaning beyond that, so the 3 baseline for a fully documented schema is the correct score.

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 opens with a specific verb and resource ('List the eSIMs in the user's connected Simvito account') and enumerates exactly what each entry contains: destination, plan, status, installed state, data left, expiry and a management link. That account-scoped read is unmistakably different from every sibling (search_plans, find_destination, start_checkout and the rest are all pre-purchase plan tools), so an agent can route without opening a 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?

It states a hard precondition – 'Requires connecting a Simvito account' – which is the main thing that can make this call fail or be inappropriate, and it implicitly scopes usage to the user's own existing eSIMs rather than plan shopping. It does not name a sibling alternative or an explicit when-not condition, but none of the listed siblings offers overlapping functionality, so nothing important is left ambiguous.

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