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

No annotations are provided, so the description carries the full burden, and it does useful work: it discloses the return shape (points of [RFC3339 time, value] pairs), that values may be string/number/null, and the exact not-found error 40405. It omits auth/permission or rate-limit context, so not 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?

Brief and front-loaded, with the core purpose stated in the first clause followed by return/error details. Slightly awkward indentation and line breaks, but no wasted sentences.

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 usefully fills the gap by describing the points structure and error behavior, and the schema covers the date/granularity defaults. Adequate for a 5-parameter read tool, though date-range interaction with granularity could be spelled out more.

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 the baseline is 3; the schema already documents symbol, type, dates and granularity. The description adds only a marginal note (no metric parameter) rather than new parameter semantics.

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 PE values') and implicitly distinguishes itself from the sibling get_valuation_latest by stressing history. It does not explicitly name the alternative, so it stops short of a 5.

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?

Clarifies a constraint ('no metric selector is supported') which preempts a likely wrong expectation, but gives no positive when-to-use guidance or explicit routing to get_valuation_latest. Usage is only implied.

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