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

The annotation readOnlyHint already indicates a safe read operation. The description adds meaningful context beyond that: the id format requirement (no prefix vs uuid-) and the underlying Recurly REST endpoint. 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?

Two concise sentences with no filler. The key id-format rule is front-loaded, and the endpoint reference is a helpful one-line addition.

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 one-parameter read-only fetch, the description plus annotation and schema are sufficient. It covers what is fetched, how to identifier it, and the safety profile. No output schema means return-format details are not required.

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%, so the schema already documents the parameter semantics fully. The description restates the same id/uuid guidance and adds the REST path, but does not provide substantive new parameter meaning.

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 states a specific verb and resource: "Fetch one subscription by its id or uuid." It clearly identifies what the tool does and distinguishes it from sibling tools like cancel, pause, or list subscriptions.

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 usage is implied: use this tool when you have a subscription id or uuid and want that single subscription. However, it does not explicitly contrast with alternatives like list_subscriptions or state when not to use it.

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