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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the bar is lower; the description still adds two genuinely useful facts not in annotations: the master API key requirement and the per-request price. It stops short of 5 because it says nothing about rate limits or failure modes for a privileged read.

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 operative text is two front-loaded sentences with zero waste. The embedded pricing HTML block is boilerplate rather than explanatory content, which slightly dilutes an otherwise tight definition.

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?

An output schema exists so return values need not be described, and the description covers auth and cost. What is missing is routing context against the many sibling account tools, which is the main gap for an agent deciding whether to call this one.

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% with a single documented 'Account ID' parameter, so the schema already carries the semantics. The description only restates 'by ID' and adds no format, source, or lookup guidance beyond it.

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 ('View an account by ID'), which clearly separates it from the write siblings like patch_apollo_accounts_account_id and post_apollo_accounts_search. It does not explicitly name an alternative, so it stops short of a 5.

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 only guidance is the prerequisite 'Requires a master API key'. There is no indication of when to use this versus post_apollo_accounts_search or the other account-related siblings, and no exclusions or conditions.

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