Portfolio performance

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

Annotations already declare readOnly/idempotent/non-destructive and openWorld. The description adds genuine behavioral context beyond that: the source is 'Thndr's returns chart', granularity varies (daily/weekly), and periods may be 'only partly covered' — a caveat an agent would otherwise not know. It stops short of explaining auth or error behavior.

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?

A single front-loaded sentence that leads with the resource and periods before enumerating return fields. Dense but every clause describes a distinct returned value; no filler or repetition of the name/title.

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 compensates by enumerating the returned fields and caveats. For a one-optional-parameter read tool whose safety profile is covered by annotations, this is close to sufficient; only the auth/account prerequisite and cross-tool routing are absent.

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?

One optional parameter with 100% schema description coverage — the enum values and market mappings are already documented in the schema, so the baseline is 3. The description adds nothing about the market parameter's effect on returned data.

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?

Names a specific resource (portfolio performance) with concrete scope: a fixed set of periods (1D–2Y) and an enumerated set of returned metrics. This distinguishes it from data-returning siblings like get_price_performance and get_realized_returns, though it never names an alternative explicitly.

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?

The description states what comes back but never says when to choose this tool over get_price_performance, get_portfolio_allocation, or get_realized_returns, nor does it state prerequisites (e.g., authenticated account with positions). No exclusions or context cues are given.

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