b2_report_usage_growth

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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial behavior beyond that: it fetches only the two compared snapshots for speed, returns the two dates plus per-account start/current GB and % growth, flags new accounts, scopes by the caller's key, and requires Usage Reports enabled. Nothing contradicts the annotations.

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?

Five dense sentences, front-loaded with the core purpose; each sentence earns its place (purpose, use-cases, mechanism/efficiency, output shape, scope+precondition). No filler and no repetition of what the schema already states.

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 supplies the needed return-shape info (dates compared, per-account start vs current GB, % growth, new-account flag). It also covers the prerequisite, scope, data source, and performance behavior, so an agent can select and invoke the tool correctly with no gaps.

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%, so the baseline is 3; the description earns a 4 by giving the period/days parameters operational meaning — the comparison against 'one month/quarter/year earlier' using end-of-day stored_gb snapshots and the 'fetches only those two days' performance rationale — context the schema's per-parameter descriptions don't provide.

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+resource ('Rank accounts by how much STORED data grew or shrank between two points in time') and names its data source (daily B2 usage reports, stored_gb end-of-day snapshot). The example queries ('which customers grew the most/least', 'who's moving data off') make its niche unmistakable, and it is clearly distinguished from sibling b2_rank_egress_leaders, which ranks by egress rather than stored-data growth.

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 explicit use-case phrasing ('For "which customers grew the most/least", "who's moving data off"'), a hard precondition ('Needs Usage Reports enabled'), and scope semantics ('Scope follows the caller's key'). However, it never names an alternative tool or states a when-not condition, so it stops just short of a 5.

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