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

Annotations already establish readOnly=true, destructive=false, openWorld=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: 'No sign-in needed,' which is an authentication prerequisite the annotations do not capture. It still omits pagination/return-shape details, so not 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?

Front-loaded with the key differentiator ('No sign-in needed') then purpose, then routing, and every sentence carries weight. The routing sentence is dense with tool names but each is load-bearing for a multi-persona workflow, so it stays useful 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 no output schema, the description does describe what comes back (apps/services in stock, per country, with price in credits) and covers the auth and safety context via annotations. It is complete enough to call correctly, missing only explicit error/empty-result behavior.

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 each of the three parameters documented (search, country filter, limit for max countries). The description only loosely echoes these ('by country'), adding no syntax or format detail beyond what the schema already provides, so the 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?

The description gives a concrete verb (search/find) and resource (which apps/services have virtual numbers in stock, by country, with price in Ucode credits), which is more specific than the title alone. It distinguishes itself from renting siblings by flagging the no-sign-in scope and positioning itself as the discovery/quote step, though it never explicitly contrasts with the similarly named ucode_sms_prices sibling.

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 explicit routing: 'Use this first whenever someone asks for a number or a price,' then names the exact next-step alternatives for two distinct caller personas (signed-in humans vs autonomous agents). An agent knows both when to pick this tool and where to go afterward without opening other schemas.

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