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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered; the description adds meaningful context on top: a stated cost ($0.02) and a clear inventory of what the response contains (drivers with direction and weight, plus a one-sentence summary). It stops short of disclosing freshness/caching behavior or any rate/credit limits for repeated calls.

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?

Front-loaded with the question the tool answers and the price, then a single dense sentence enumerating sources and output shape. Every clause carries information; nothing is redundant with the title or annotations.

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 burden of describing the return and does so concretely (15-minute move, per-source drivers with direction and weight, one-sentence summary) plus asset coverage and cost. Minor gaps remain: no statement of data freshness/latency or what happens for illiquid/unsupported symbols.

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?

Only one parameter, and the schema documents it at 100% coverage with examples (ETHUSD, NVDA, TSLA). The description still adds value by naming the accepted asset universes (crypto, tokenized stocks, US stocks), which tells the agent the symbol namespace is cross-asset rather than crypto-only.

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?

Opens with a specific framed question ('Why is a symbol moving?') and states exactly what is produced: the 15-minute move plus its likely drivers broken out by source (on-chain flow, unusual activity, smart money, perp crowding, news, SEC filings, insiders). An agent can distinguish this diagnostic/attribution tool from data-dump siblings like market.snapshot or market.summary without opening the 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 'Why is a symbol moving?' framing implies when to reach for it, and asset coverage ('Crypto, tokenized stocks and US stocks') is stated, which helps route requests. However, there is no explicit when-not guidance, no mention of alternatives (e.g. market.summary for a plain price recap), and no note on the 15-minute window being the fixed horizon versus longer-horizon tools.

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