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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so safety is covered. The description adds real value beyond that: first purchase occurs at the selected start month-end, omitted dates use calculator defaults clamped to coverage, and no account access or order execution. It stops short of describing rate limits or full return shape, but the added behavioral detail is substantial.

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?

Reasonably front-loaded, but the sentence 'Returns data metadata and the free calc-dca PNG' is immediately followed by a near-duplicate 'Returns results, conditions, assumptions, an editable link, share page and PNG,' which wastes space and blurs the return-value statement.

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 an output schema present and annotations covering the safety profile, the description needs only the sourcing caveat, timing rule, and default-handling note, all of which are present. It is largely complete for a no-required-parameter read-only backtest tool.

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 all 10 parameters are fully documented in the schema, establishing a baseline of 3. The description largely restates those fields (ticker, start/end YYYY-MM, deposit USD, monthly USD, frequency, fee, benchmark, return basis) without adding format or constraint detail beyond what the schema and pattern/enum already supply.

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?

Opens with a specific verb+resource ('Dollar-cost-averaging backtest') and immediately scopes it ('using installed monthly closes, not live quotes'). An agent can distinguish it from siblings like compound_interest or historical_return without opening any 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?

Implies the use case through the 'installed monthly closes, not live quotes' constraint and the DCA framing, but never states when to choose this over compound_interest or historical_return. No explicit alternatives or exclusion conditions are named.

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