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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), and the description goes beyond them by disclosing the paywall behavior, the pro_required fallback, and the exact aggregate fields returned. It does not discuss rate limits or latency, but the access model is unusually well disclosed.

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 dense sentences with the core behavior front-loaded and the access constraint second. Nothing is wasted, though the second sentence packs paywall, fallback, and a flag name together tightly enough to be slightly hard to parse.

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 enumerates the return aggregates and the pro_required fallback, which is what an agent most needs. It omits edge cases (invalid MM-DD, windows crossing year boundaries, empty history) but is complete for normal invocation.

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 67%, and the schema already documents start/end as MM-DD and the asset enum. The description restates the MM-DD format but adds no new semantics such as window-length limits, timezone handling, or year range, so it does not compensate for the coverage gap.

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+scope: past-year returns over a calendar window defined by start/end MM-DD, and enumerates the outputs (average, median, % of years up, best/worst years). This is clearly distinguishable from siblings like day_seasonality and monthly_seasonality 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?

It conveys when the tool is free (S&P 500 windows inside the current month) versus when it degrades to covered months plus a Pro link, which is real usage context. However, it never says when to prefer this over monthly_seasonality or day_seasonality, so routing between the seasonality siblings remains inferential.

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