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

Annotations only declare readOnlyHint and openWorldHint; the description adds the genuinely useful behavioral facts an agent needs — the call costs $0.05 USDC and requires payment. It does not restate safety traits already in annotations. Minor blemish: 'No parameters' understates the optional api_key path, but that path is fully documented in the schema.

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?

One dense sentence front-loaded with the price, followed by the returned content list. No filler, and the cost — the most decision-relevant fact — comes first.

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 must enumerate the payload, and it does: raw per-component metrics, 30-day history, 7-day trend, and methodology with weights/thresholds/sources. Combined with the schema's payment documentation this is sufficient to call correctly; only the 'No parameters' phrasing slightly muddies an otherwise complete picture.

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 optional api_key (prepaid key vs catalog pass vs x402 payment) is already fully explained in the schema. The description contributes nothing about it and in fact says 'No parameters,' which is a small inaccuracy rather than an aid. Baseline 3 applies when the schema does all the work.

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 deliverable (full market-regime report) and defines it as a superset: 'Everything in regime_now plus raw metrics for every component, 30-day score history, 7-day trend and full methodology.' Naming regime_now directly lets an agent place this tool relative to its sibling without opening either schema.

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?

The 'everything in regime_now plus...' framing implies the selection rule (take the full version when you need history/trend/methodology) and the price is called out so cost trade-offs are visible. It never explicitly says when to prefer regime_now or free_regime instead, so the routing rule is implied rather than stated.

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