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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, and the description adds genuinely useful behavior: the data is stored/cached and read with "no call to ACE Music," meaning values may be stale. It also specifies the return shape (object keyed by account email) and the underlying endpoint, though it does not say what happens for a token with zero accounts.

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?

Three tight sentences: what it returns, the freshness caveat plus alternative, then the response shape and endpoint. The most decision-relevant information (stored/no live call) is front-loaded with no filler.

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 and no parameters, the description carries the burden and does so: it names the returned fields, the object keying, and the cached nature of the data. An agent can call this and interpret the result without further documentation.

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 tool takes no parameters, so the baseline is 4 by rule. The schema coverage is 100% and the description correctly implies there is nothing to configure beyond the token's scope, though it never explicitly says the account set is fixed by the token.

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 (list the ACE Music accounts for this useapi.net API token) and enumerates the returned fields (plan, maxJobs, health). It is clearly distinguishable from acemusic_get_account, which is named as the tool for live data.

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?

"Use acemusic_get_account for live credits" explicitly routes the agent to the sibling when freshness matters, which is the key selection decision here. It stops short of stating when-not to use this tool (e.g., it is not a diagnostics tool), but the routing guidance is clear.

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