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

The readOnlyHint annotation already signals that this is a safe, non-mutating operation, so the bar is lower. The description adds useful context by documenting the id-without-prefix and code- prefix conventions and the underlying REST endpoint, but it does not disclose any further behavioral details such as error responses, pagination behavior, or field selection. This is acceptable but not enriched beyond the annotation.

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 carry all the necessary information with zero redundancy. The core action is front-loaded, the id formats are packed with examples, and the endpoint reference is separate and terse. Every sentence earns its place.

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 single-parameter read operation, the description covers the primary usage details: what it fetches, the accepted identifiers, and the underlying API call. The readOnly annotation covers the safety profile, and the schema fully documents the parameter. A minor omission is the absence of any mention of the response structure or not-found behavior, but for a simple GET-style tool this is not a significant gap.

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 input schema already covers the lone account_id parameter with a description that matches the prefix convention, so schema coverage is 100%. The description reinforces that with concrete examples ('e28zov4fw0v2', 'code-bob') and the API path, but it does not add meaning beyond what the schema already provides. Baseline 3 is appropriate.

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 begins with a specific verb and resource, 'Fetch one account by its id', and clarifies the two accepted identifier formats. It implicitly distinguishes this from the sibling list_accounts by specifying a single account fetch, and cites the exact Recurly API endpoint, leaving no ambiguity about the operation.

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 gives clear context for when this tool applies (fetching a single account by id or code) and provides concrete examples of valid inputs. It does not explicitly name alternatives or state when not to use it, but the 'one account' framing makes the intended use clear in contrast to listing or subscription operations.

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