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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds valuable behavioral context by listing the rich set of data returned (fees, tethering, SIM costs, price history, etc.), which helps the agent know what to expect from the call.

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 purpose and followed by the actionable hint about where to get the id. The first sentence is a dense list of returned fields, but each item earns its place by informing the agent about output contents; there is no wasted wording.

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?

Given the simple one-parameter signature, full schema coverage, and annotations that cover safety behavior, the description is complete. It compensates for the absence of an output schema by enumerating what data is returned and explains how to obtain the required id.

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 id parameter is well defined with a format example (e.g., joytel-617). The description adds meaning by specifying that the id should come from search or search_plans results, which is not stated in the schema and clarifies the value's origin.

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 (Fetch) and resource (one plan by id), then enumerates the returned data fields. It also directly names the sibling tools that produce the required id (search, search_plans), making it clearly distinguishable from search-style tools.

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 tells the agent to insert an id obtained from search or search_plans results, which provides clear context for when to use this tool. It does not state when not to use it or list alternative tools, but the intended workflow is unambiguous.

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