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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful non-annotation context about authentication: the key is taken from the X-API-Key header of the MCP request or the apiKey argument. It stops short of describing failure behavior when no key is supplied, which would have pushed this higher.

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?

One sentence, front-loaded with the returned data before the auth mechanics. The only waste is the unexplained 'Free:' fragment at the start, which reads as leftover tier labelling rather than 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?

An output schema exists, so return-value explanation is not needed, and the annotations carry the safety profile. The description covers the remaining essentials: what is returned and how the credential is supplied. A brief note on error behavior without a key would make it fully complete.

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 optional parameter, so the baseline is 3. The description adds marginal value by indicating the apiKey argument is a fallback to the request header, but it does not spell out precedence, format expectations, or what happens if both disagree.

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 names a specific verb-plus-resource pair (retrieve status of the MoneyTools API key) and enumerates exactly what is returned: plan expiry, daily call usage against the 1,000/day cap, and remaining prepaid credits. This clearly separates it from siblings such as plan_buy or allowance_setup. The stray leading 'Free:' fragment is unexplained and slightly muddies an otherwise precise statement.

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?

Usage is only implied: an agent can infer this is the tool to call for account/quota information, but the description never says when to prefer it over plan_buy or allowance_setup, nor does it state prerequisites or when-not-to-use. There are no explicit alternatives named.

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