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

Annotations already establish the safe read-only, idempotent, non-destructive profile, so the bar is lower. The description adds real value beyond them: the data provenance (connected subscription sources such as Stripe) and the null semantics for churn rates when a month starts at zero, which an agent would otherwise misread as zero churn.

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?

It opens with the resource and its scope, then the field list, then the alternative tool – good front-loading. The inline formula and long enumeration are dense but each element earns its place by defining the output without an output schema; the second sentence is a slightly abrupt topic switch to get_metric.

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 full burden of describing return values, and it does so exhaustively: all movement components, the reconciliation formula, customer counts, churn rates and their null condition. Combined with the schema's complete parameter documentation, an agent has everything needed to call and interpret this tool.

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% and all three parameters (from, to, company) are documented in the schema itself, including defaults and the "all"/"Personal" values, so the description need not repeat them. The description adds no parameter-level syntax or constraints of its own, making the baseline 3 appropriate.

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 the exact resource (monthly recurring revenue movements per month, counted per customer) and enumerates every returned component: start, new, expansion, reactivation, contraction, churn, end, customer counts and churn rates. It even gives the reconciliation identity (start + new + expansion + reactivation − contraction − churn = end), so an agent knows precisely what the tool computes and how it differs from get_metric.

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?

It explicitly routes to the sibling: get_metric gives mrr, mrr_churn_rate and net_new_mrr for the last complete month, implying this tool is for month-by-month breakdowns over a range. That is clear contextual guidance, but there is no explicit when-not or prerequisite statement (e.g. what happens when no subscription source is connected).

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