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

The description 'Retrieve' aligns with the readOnlyHint annotation, but it adds no additional behavioral context beyond what the annotation already provides. No contradictions.

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 extremely concise: two sentences with no redundant information. It front-loads the purpose and provides the API reference efficiently.

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 simple retrieval tool with a single required parameter, no output schema, and a readOnlyHint annotation, the description is fully complete. It tells the agent everything needed to invoke the tool correctly.

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?

The description reinforces the parameter role ('by code') and adds the API endpoint structure ('GET /plans/{code}'), which provides extra context beyond the schema description. Schema coverage is 100%, so baseline is 3; the added endpoint detail justifies a 4.

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 clearly states the verb 'Retrieve', resource 'single plan', and the method 'by code'. It distinguishes from list plans by specifying 'single' and includes the API endpoint for additional context.

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 usage (fetch a specific plan by code) but does not explicitly state when to use this tool versus alternatives like lago_list_plans, nor does it provide when-not or exclusion criteria.

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