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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safe-read nature is covered. The description adds the scoping fact that exactly one plan's details are returned, which is useful, but it does not disclose other behavioral traits such as error conditions, rate limits, or authentication requirements. No contradiction with annotations.

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?

The description is a single, tight sentence that front-loads the core concept ('Details of one plan') and then lists the included attributes. There is no redundancy, filler, or unnecessary context; every element contributes to the agent's understanding.

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?

No output schema exists, so the description's enumeration of return fields (data, validity, network, 5G, top-up, carriers, price, checkout link) provides a useful outline of what to expect. The main gap is a potential overlap with the sibling tool get_purchase_link: the description mentions a checkout link without clarifying how that relates to the dedicated purchase-link tool, creating mild ambiguity.

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 67%: days and lang are documented in the schema, but plan_id has no description. The tool description itself provides no additional parameter meaning, so it does not compensate for the undocumented plan_id or deepen understanding of the existing parameter descriptions. Baseline of 3 is appropriate given partial schema coverage.

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 identifies the resource ('one plan') and enumerates its content (data, validity, network, 5G, top-up, carriers, price, checkout link). It implicitly distinguishes from siblings like search_plans (which would return multiple plans) and recommend_plan (which suggests a plan), though it lacks an explicit verb like 'retrieve' or 'get' within the description itself.

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?

The description implies use for fetching details of a single plan, but it provides no explicit guidance on when to choose this tool over alternatives. It does not mention sibling tools such as search_plans or get_purchase_link, leaving the agent to infer the appropriate context from the title and schema alone.

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