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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuine behavioral context beyond them: it discloses the returned fields (window, series of time/price/volume), the default window of 1d, and the failure mode that absent chart data returns not found.

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 sentences, front-loaded with the action and its unusual parameter contract, then return behavior, then sibling routing. Dense but every sentence carries information; no filler.

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, return-value documentation is not required, yet the description still summarizes the shape and the not-found case. Purpose, usage, alternatives, defaults, and error behavior together cover everything needed to invoke this tool correctly.

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 per-parameter meaning is already documented (baseline 3). The description adds value by showing how the params combine ('AAPL + NASDAQ or BTC + USD with is_crypto=true'), clarifying the first/second pairing semantics and the role of is_crypto beyond the individual field descriptions.

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 (Fetch) and resource (Google Finance historical price and volume points) and pinpoints the unusual input shape it requires: separate first/second legs like AAPL + NASDAQ or BTC + USD. It explicitly differentiates itself from google_finance_chart and google_finance_quote, so an agent can route between them without opening schemas.

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 the triggering condition (instrument supplied as separate first/second legs) and names two alternatives with the condition that selects each: google_finance_chart for a combined quote identifier, google_finance_quote for a current overview. Both when-to-use and when-to-prefer-something-else are present.

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