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

readOnlyHint=true already declares the safety profile, so the description does not need to argue non-mutation. It adds genuine value with 'for the authenticated user', signaling per-user data scoping, but says nothing about behavior when the ID does not exist or belongs to another user.

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?

A single front-loaded sentence with no filler. Every clause (verb, resource, identifier, user scope) carries information.

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 single-parameter read with annotations covering safety and full schema documentation, the essentials are present. However, with no output schema, the description does not indicate what is returned (a postcard object and its fields) or how missing/unauthorized IDs are handled, which would help an agent interpret results.

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 schema already documents the single 'id' parameter with an example format (pc_abc123). The description adds only that the ID identifies a postcard, which the schema already conveys, so 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?

States a specific verb and resource ('Retrieve one postcard by ID') and adds scope ('for the authenticated user'). It implicitly distinguishes itself from list-postcards-tool by returning a single postcard, but never names that sibling or any other, so differentiation is inferred rather than stated.

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 phrase 'by ID' implies it is the right tool when a postcard identifier is already known, versus the listing tool otherwise. There is no explicit when-to-use/when-not or named alternative, so guidance is only implied.

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