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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable context beyond annotations: the paid per-call cost ($0.75–$2.00) and the fact that it runs on 'real historical data', which informs the user about data semantics. No contradiction with annotations.

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 sentences, first is packed with the core purpose and modes, second is a concise pricing/alternative note. Every word earns its place, no fluff or redundancy.

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?

The description covers the main modes and pricing but omits two important contextual elements: there is no output schema, and the description does not mention what the backtest returns (e.g., performance metrics, equity curve). It also silently drops the 'engine' mode listed in the schema enum. For a paid, multi-mode tool, this leaves meaningful gaps.

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 description adds meaning above the schema by explaining that 'strategy' can be a plain-language description or a template name, and by mapping the 'kind' values to the described modes (custom, standard, optimize). This enriches parameter understanding without duplicating schema text.

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 'Backtest a trading strategy on real historical data', a specific verb+resource pair that clearly distinguishes this tool from the analysis/forecast siblings. It further clarifies three distinct modes (plain-language custom backtest, standard template, parameter optimization), leaving no ambiguity about what the tool does.

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 explicitly tells users when to use the tool ('describe rules in plain language', 'run a standard strategy template', 'optimize parameters') and when not to ('Free alternatives exist for several of these — see list_einstein_capabilities'). This provides both inclusion and exclusion criteria, plus a pointer to alternative tools.

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