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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and network-boundary behavior are covered. The description adds the meaningful distinction that this returns share-count data while shares_full returns historical shares-out rows, though it does not describe caching, latency, or freshness of the data.

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?

Two sentences, zero filler. The primary action is front-loaded and the disambiguation clause follows immediately; every sentence earns its place.

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?

An output schema exists, so return values need not be described. For a one-parameter, read-only lookup with annotations covering safety and network scope, the description supplies everything an agent needs to call it 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% and the single symbol parameter is already documented with an example (AAPL), so the schema carries the semantics. The description only restates 'one symbol' without adding format or constraint detail beyond the schema, which is the baseline for fully-covered schemas.

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), a precise resource (Yahoo Finance share-count data), and a scope limit (one symbol). It also names the sibling yahoo_finance_ticker_shares_full and how it differs, so an agent can distinguish the two 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?

Gives an explicit routing rule: use yahoo_finance_ticker_shares_full when historical shares-out rows are needed, implying this tool covers the current/point-in-time share count. The alternative and its selection condition are both stated.

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