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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description is free to add the traits that matter: the 24h window for crypto, the delayed nature of stock quotes, the upstream sources, and the 'news and data only, not advice' scope limit. Minor gap: nothing about ranking methodology or how stale a headline can be.

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?

A single dense opening sentence front-loads what the tool returns, followed by a short scope disclaimer that earns its place for a financial tool. No filler, no restatement of the title.

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 an output schema present, the description needn't explain return shape, and it correctly covers the two markets, the direction options, and the sourcing. It stops short of explaining feed cadence or how 'movers' are ranked, a small gap for a data-discovery 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%, so all three parameters (limit, market, direction) are already documented with enums and defaults, making 3 the baseline. The description adds only context about the market values (crypto = 24h CoinGecko, stocks = delayed US), not new syntax or constraints.

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-and-resource outcome (top gainers/losers) plus the data sources (CoinGecko 24h crypto, delayed Yahoo/Nasdaq stocks) and the enrichment (a sourced headline naming each mover). An agent can distinguish it from get_asset_news, which returns headlines for a specified asset rather than ranked movers.

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?

Usage is implied by the description: use it for a broad market-movement snapshot rather than per-asset news. However, it never names get_asset_news or any sibling as an alternative, nor states when this tool should not be used, so the agent must infer the boundary itself.

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