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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open world), so the bar is lower. The description adds genuinely new behavior: it reads the live published catalog with a labeled snapshot fallback, which tells the agent about data freshness and possible staleness not encoded anywhere else.

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, front-loaded with the trigger condition and no filler. The trailing parenthetical about snapshot fallback is terse but earns its place; nothing is redundant or bloated.

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 and annotations covering safety, the description only needs to supply trigger, scope, and any non-structured behavior — it does all three. The remaining gap is routing relative to sibling plan-discovery tools, which is left entirely implicit.

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 100% with three enums fully documented, so the schema already carries parameter meaning. The description mirrors the filter set (type, max price, min GB, coverage scope, per-GB) without adding syntax, defaults, or edge-case notes beyond the schema (e.g. that fair-use plans always match min_gb). 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+resource (browse/filter esimgomobile plans) and enumerates the filter dimensions it supports, so the agent knows exactly what the tool returns. It does not, however, distinguish itself from close siblings like list_available_plans, compare_plans, or recommend_plan.

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?

Opens with an explicit trigger phrase ('Use when the user wants to browse or filter...'), which is clear usage context. It gives no exclusions or sibling alternatives, so an agent must still guess whether compare_plans or list_available_plans is the better call for a similar request.

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