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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real behavioral substance on top: the $5 floor, the 50%-below-high threshold, the `low_scope` all-time caveat for newer cards, and that figures are USD. It says nothing about ordering, pagination, or what `limit` truncates, which keeps it from a 5.

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, front-loaded with the trigger, then the qualifying rules, then the returned fields — no filler. The `low_scope` parenthetical is the only mildly dense spot, but it earns its place by heading off a data-interpretation error.

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, the description doesn't need to enumerate return fields, yet it usefully names 'the high and the percent below it, in USD'. Combined with the threshold rules and the all-time-scope caveat, an agent has enough to call this correctly; only result ordering/limit semantics are absent.

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% and the game enum is fully documented in the schema, so the schema carries parameter meaning. The description only reinforces that results are scoped to 'one game'; it adds nothing about `limit` (default 25, max 200) or which parameter it affects. Baseline 3 is appropriate.

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 and resource ('which cards in one game are at their lowest price or have crashed') and pins down the exact qualifying criteria: $5+ market price, at least 50% below the high. It never names the obvious counterpart sibling (all_time_highs) or distinguishes itself from movers, so sibling differentiation is left implicit.

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 opening clause gives a clear triggering condition ('when the user asks which cards ... are at their lowest price or have crashed'), which is enough to route most calls correctly. It stops short of stating when NOT to use it — e.g. that all_time_highs is the mirror tool for the opposite question.

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