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

Annotations already declare readOnlyHint=true, so the description only needs to add non-safety context. It adds value by noting this is a 'Free canonical tool,' clarifying it operates on historical records, and providing filter-style expectations (year-based rather than ISO dates). No contradictions 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?

Three sentences, each earning its place. First sentence states what it does and cost status, second gives primary use cases, third provides indispensable filter guidance. No repetition of schema details, 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?

With 6 parameters, nested objects, and no output schema, the description covers the essential decision points: purpose, historical scope, use cases, and filter style. It doesn't describe return shape, but the mention of 'metrics' and 'top-event lookups' implies enough for an agent to select the tool correctly. Slightly more detail on output would push to 5, but current coverage is solid.

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 baseline is 3. The description goes beyond the schema by clarifying that volcano queries 'normally use year-style time filters rather than ISO date strings,' which directly informs how to fill the 'filters' parameter. It also gives concrete metric examples ('event_count', 'VEI'), adding semantic color to a fully documented 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?

The description uses a specific verb ('Queries') and names the resource ('volcanoes_events') with clear scope ('historical eruption records and volcanic activity metrics'). It distinguishes itself from siblings by emphasizing 'historical' vs. live events, and explicitly lists what it's 'best for' (eruption counts, VEI thresholds, top-event lookups).

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 provides concrete use cases ('Best for eruption counts, VEI thresholds, and top-event lookups') and gives practical guidance on year-style time filters over ISO date strings. It clearly implies historical data context, differentiating it from get_live_volcano_events, though it doesn't explicitly name alternatives or exclusions.

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