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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds meaningful non-obvious behavior: keys are returned as prefixes only, never secrets, and paid plans have no monthly cap unless the person sets one.

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-loaded and clear, but the full pricing schedule (dollar amounts, per-1,000 overage rates) is longer than needed to select or invoke a read-only account tool. That block serves interpretation of the returned plan, not invocation, and crowds out more actionable guidance.

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 carries the return-value burden and does so by listing the fields returned and the key-prefix caveat. It also handles the empty state. Minor gaps remain around error cases for an invalid account_id, but nothing essential is missing for a one-parameter read.

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 is already documented as optional with 'omit to list all'. The description's 'or read one with its plan...' restates that branch rather than adding syntax or edge-case meaning, so the 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 and resource ('list the API accounts ... or read one') and enumerates exactly what a read returns: plan, usage, monthly cap, key prefixes. It also distinguishes itself from siblings by naming the api_ family and its role as the prerequisite lookup.

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?

Explicitly says 'Use it before the other api_ tools to get account_id and key_id', giving both the ordering and the reason. It also covers the no-account case and points to the signup URL, so the agent knows what to do when the tool returns nothing useful.

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