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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds the exact return columns and the error behavior ('Unknown run_id -> not_found'), which is useful context beyond annotations, though it does not discuss ordering, limits, or empty results.

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 tight sentences front-load the return shape, then the error behavior. Every sentence earns its place with no filler.

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 simple, read-only comparison tool with rich annotations and no output schema, the description is nearly complete: it enumerates the returned columns and states the not_found behavior. It falls short only on edge cases like empty run_ids or duplicate handling.

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 0%, so the description must compensate. It does clarify that run_ids refer to 'previously run backtests in this session' and that unknown IDs produce not_found, but it leaves ambiguity around array ordering, duplicate IDs, and maximum length. This is partial compensation for undocumented parameters.

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 states a specific verb ('Returns a table') and resource (backtest metrics) and scopes it to 'previously run backtests in this session', which implicitly distinguishes it from run_backtest. It does not explicitly name an alternative sibling, but the scope is clear enough for an agent to understand what it 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 phrase 'for previously run backtests in this session' implies when the tool is applicable, and the not_found behavior gives a hint about input validation. However, there is no explicit guidance on when to prefer this over run_backtest or other comparison tools, and no exclusion conditions are given.

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