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

Annotations already establish the safe read profile (readOnlyHint=true, destructiveHint=false), so the bar is lower. The description adds a concrete auth prerequisite ('Needs the user's Cotlet API key with access to this app') and clarifies the response shape, both useful beyond the structured fields.

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?

Front-loads the identity of the resource and keeps to four short sentences. There is mild redundancy between the first sentence (contact details, tax fields, links) and the second (which re-lists the same fields), but nothing wasteful enough to impede the agent.

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?

With no output schema, the description correctly compensates by listing the fields a caller can expect. Combined with annotations covering safety and the mention of the API key requirement, an agent has enough to invoke it correctly; only pagination/edge behavior is untouched, which is irrelevant for a single-record fetch.

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 parameter account_code already carries a description ('Account code from list_accounts'). The description restates 'by account_code' but adds no syntax or sourcing detail beyond the schema, 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+resource ('Returns one account by account_code') and enumerates the fields returned (name, company, email, address, VAT number, tax exemption, state). The 'one account' framing implicitly distinguishes it from the sibling list_accounts, though it never names that sibling explicitly.

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?

Gives a clear use context: 'Use it to see who the customer is before you change a subscription or refund an invoice,' which ties it to mutation siblings like recurly_change_subscription and recurly_refund_invoice. It lacks an explicit when-not or a named alternative such as list_accounts.

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