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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context beyond that: results are per SMS part and per mobile network (not a single blended price), and the backing call is a legacy GET /prices.

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?

One sentence, front-loaded with the verb and resource, then the estimation use case, then the API endpoint. Zero filler and nothing an agent must skip past to get the 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?

For a single-parameter, read-only pricing lookup with no output schema, the description tells the agent what comes back (per SMS part, per mobile network) and why it matters. Minor gaps remain around currency and whether partial prices are returned for networks without coverage, but nothing blocking.

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% and the single 'country' parameter is fully documented in the schema (ISO 3166-1 alpha-2, with examples EE/GB). The description only restates that pricing is for 'one country', adding no syntax or constraint detail beyond the schema. Baseline 3 is appropriate.

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 ('Get this account's price per SMS part') and pins down the exact granularity (one country, per mobile network), which separates it from siblings like get_balance or get_statistics. The parenthetical cost-estimation framing makes the intent unmistakable.

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?

Explicitly routes the agent: 'use it to estimate what messente_send_sms will cost', naming the sibling that consumes this data. It lacks a negative case (e.g., when to call get_balance or lookup_numbers instead), so it stops short of a 5.

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