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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered; the description instead adds genuinely useful domain behavior: $0.10 per additional monitor for e-mail alerts, trial post-expiry alert limits to the ten oldest monitors, and the warning that this value is authoritative over documentation. It does not describe response shape or refresh timing, but the behavioral context is well above the annotation baseline.

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 with what is read, followed by cost and gating rules; no filler sentences. Slightly penalized because the final sentence is long and the phrase 'it is the number IN FORCE, not the documentation's' is cryptic on first read.

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?

For a zero-param, read-only tool with no output schema, the description covers what the call returns, the pricing rules that make the numbers actionable, and the trial-expiry consequence. The only gap is that the concrete response fields are listed loosely rather than as a shape, which matters slightly given there is no output schema.

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 zero parameters, so per the baseline there is nothing the description must compensate for. The description correctly spends no words on argument semantics and instead uses the space on result meaning.

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 opens with a specific verb ('Read') and enumerates the exact resources returned: free allowances, billing-disabled options, prices, and the account's 7-day trial. It is clearly a billing-state reader, distinct from write-side siblings like buy_plan/cancel_plan, though it never explicitly distinguishes itself from `pricing` or `list_plans`.

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 an explicit trigger: 'Check before creating the second monitor or lowering the interval,' which tells the agent precisely when this tool is the right call. It also names a fallback endpoint (`GET /api/plans`) for monitors that need a plan, though it does not state any when-not-to-use condition.

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