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

Annotations already declare this a safe read (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the burden is lighter — and the description adds genuinely useful behavior beyond them: $0.10 per call via x402, Builder/Pro Agent key requirement, a 1-call/day free trial restricted to MCP, and a 90-day lookback window. Cost and auth disclosure of this kind is exactly what an agent needs before invoking. It stops short of describing failure modes when the lookback is exceeded or the key is invalid.

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, front-loaded with the purpose question before pricing and scope. The pricing sentence is the longest but earns its place by covering three distinct payment paths. No filler or repetition of annotation data.

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 usefully pre-announces what the payload contains — new/retired services, category share shifts, top movers, with figures on both sides — plus the cost, auth, and lookback limits for a paid tool. An agent has what it needs to decide and invoke, though ordering or response shape details are left unspecified.

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%, so both parameters (since, api_key) are already fully documented in the schema, including the YYYY-MM-DD format and 90-day cap. The description restates the date-scoping constraint but adds no format, syntax, or edge-case meaning beyond it, so the baseline of 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?

The tool is framed as a diff operation ('what changed since a date I name') over a specific resource, and it enumerates the concrete dimensions of the comparison (new services, retired services, category share shifts, top movers). That is enough to distinguish it from siblings like get_market_summary or get_liveness, though the differentiation is left implicit rather than stated.

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 gives real context for when the tool applies — 'diffs today against any snapshot up to 90 days back' — and explains the payment paths (paid per call, Builder/Pro key, one free trial/day over MCP). However, it names no alternative sibling tool and gives no explicit when-not-to-use guidance, so selection among the eleven siblings is still left to inference.

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