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

Beyond the readOnlyHint and destructiveHint annotations, the description discloses substantial behavioral detail: quarterly portfolio reconstruction, rebalancing on SEC filing lag, valuation on raw closing prices, exclusion of dividends, and a specific limitation where returns become unavailable after a captured split without a certified price basis. It also explicitly states that the window is not shortened to hide this issue, which is unusually transparent.

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 description is well-structured with four purposeful sentences: purpose/scope, methodology, return metrics, and a critical limitation. Each sentence earns its place without fluff, and the most important information is front-loaded.

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 moderately complex backtest tool with no output schema, the description sufficiently covers input modes, methodology, return metrics, and edge-case behavior. It explains what the agent can expect from the result, including the important caveat about unavailable returns, making the definition complete for a competent agent.

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 schema already documents all five parameters in detail. The description adds conceptual context by linking windowYears to trailing mode and fromDate/toDate to anchored mode, but it does not significantly extend meaning beyond the parameter descriptions already present in 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?

The description opens with a specific verb and resource: 'Backtest how cloning an institutional filer's reported 13F portfolio would have performed against a market benchmark.' This clearly identifies the tool's unique function and distinguishes it from sibling tools like GetInstitutionPortfolio or CompareInstitutionPortfolios, which provide holdings or comparisons rather than clone performance backtesting.

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 clearly establishes context by explaining that the tool can run over a trailing window or an explicit date range, with fromDate overriding windowYears. It does not explicitly name alternative tools or state when not to use this tool, but the core usage context is unambiguous enough for an agent to select it appropriately.

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