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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the description earns credit for what they can't say: it discloses that two backtests are executed internally, what is returned (both stat sets plus the delta), and the cost of one backtest. It stops short of explaining side effects such as whether runs are persisted or how long it takes.

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?

Three sentences, no filler, with the core two-run mechanism front-loaded and the universe options and cost trailing as supporting detail. Every sentence carries operational information.

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 compute-heavy tool with a nested spec parameter and no output schema, the description supplies the essentials: execution model, returned metrics, universe options, and cost. It leaves the nested spec contents mostly to run_backtest rather than spelling them out, which is a reasonable but not complete handoff.

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 100%, so the baseline is 3, but the description adds real meaning beyond the schema by naming the accepted universe values ('top500'|'top1000'|'top3000' or a symbol list) — information the schema's opaque nested 'spec' object does not provide. The as_of cutoff is left entirely to 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?

States a specific verb and resource — running a backtest spec twice under two universes — and defines the contrast precisely (point-in-time vs. still-trading names). An agent can distinguish this from run_backtest or compare_runs purely from the text, since the output (CAGR/Sharpe inflation) is also named.

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 use case is explicit (measuring survivorship-bias inflation) and it references run_backtest for the spec format, plus notes the 'costs one backtest' budget. It does not state when to skip this tool or how it differs from compare_runs, so a small inference remains.

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