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

Annotations already declare readOnly/idempotent/openWorld, so safety is covered; the description adds real value beyond them — data source and keyless access (Yahoo Finance), and the exact return composition (each day's close plus previous close and computed daily return percent). It omits rate limits/latency and the 40-symbol cap is left to the schema, so it stops short of a 5.

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?

The routing directive is front-loaded in the first words and the closing sentence reinforces the alternative. The three inline example queries are slightly redundant with the schema's examples array, which keeps it from a 5, but nothing is 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?

For a 3-param read tool with full schema coverage and annotations, the description covers purpose, alternative routing, symbol domain, and return payload shape. No output schema exists, yet the description still explains what comes back, leaving no material gap.

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 the baseline is 3, but the description adds meaning the schema does not: the accepted symbol space (indices, stocks, ^TNX yields, GC=F, BTC-USD, EURUSD=X) and its equivalence to get_quotes' symbol space. Date semantics are left to the schema.

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+resource ('historical closing prices and daily returns') with scope (specific past date or range, per symbol) and immediately contrasts with the sibling get_quotes. The worked example queries make the intent unmistakable.

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?

Explicit routing: 'PREFER for HISTORICAL...', 'Use get_quotes for CURRENT prices; this tool is for any date in the past.' The when-to-use and the named alternative are both given, and the boundary (past vs. current dates) is unambiguous.

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