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

Annotations already show readOnlyHint=true, lowering the bar. The description adds valuable context: data source ('daily Open-Meteo SST'), update frequency ('daily'), the score's construction (share of 12 regions ≥ +0.5°C plus intensity), and the caveat that it's a screening signal, not validated climatology. This goes beyond basic read-only disclosure.

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?

The description is compact—two sentences plus an update note. It front-loads the output definition, then gives trigger conditions, and ends with a limitation and freshness. Every sentence serves a purpose 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?

Despite no output schema, the description lists all return fields (marine_heat_score, warmth_level, warmest_region, per-region anomaly table). It covers data source, update frequency, use cases, limitation, and the only parameter is covered by the schema. This is complete for an agent to decide and use the tool.

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?

The only parameter 'days' is fully documented in the input schema with range (1-1825) and behavior (history vs snapshot). The description does not mention it, but with 100% schema coverage, the parameter semantics are already complete.

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 clearly specifies the tool's function: 'Returns a 0-100 global marine heat score' with detailed composition and lists four output fields. This specific verb+resource combination distinguishes it from the many unnamed sibling tools.

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?

It explicitly states when to call the tool: 'Call when the user asks about ocean warmth, SST anomalies, marine heatwaves, or coral-bleaching risk, or when timing hurricane-exposure reviews or aquaculture harvests.' It also provides a limitation ('Screening signal, not validated MHW climatology') that clarifies when not to rely on it.

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