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

Annotations already flag readOnly/openWorld/non-destructive, and the description layers on genuinely useful behavior: paid-plan gating, no pagination (full window in one call), survivorship-bias-free coverage back to 1962, weekly/monthly aggregation semantics (first open, highest high, lowest low, summed volume), and the Tiingo data source.

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 core purpose and scope, and each sentence carries information an agent needs (coverage, plan gating, row schema, flag behavior, pagination). Dense but not padded; slightly long, so not a clean 5.

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?

For a read tool with no output schema, the description effectively documents the returned row fields and their adjusted variants, coverage limits, and aggregation behavior, leaving nothing material an agent would need before calling it.

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 baseline is 3. The description goes further, explaining what adj_close is for ('use THIS for charts and return calculations'), that div_cash is tied to the ex-date, and how include_ohlc aggregates on weekly/monthly—interpretation the schema alone doesn't convey.

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 ('returns daily end-of-day closing-price history for one US-listed ticker') plus the instrument scope (stocks, ETFs, mutual funds, delisted names). This cleanly separates it from intraday quote, fundamentals, and holdings siblings without ambiguity.

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 concrete when-to-use guidance: prefer frequency='weekly'/'monthly' for multi-year ranges, and 'one call = one ticker, compare with multiple calls.' It states the PAID PLANS ONLY prerequisite. It stops short of naming specific sibling tools to prefer over this one (e.g. intraday vs daily), so 4 rather than 5.

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