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

Annotations already declare readOnly and openWorld, but the description adds genuinely useful behavior: the data refreshes monthly, and each successful call costs $0.002 via x402 on Base, Solana or Arc with failed calls uncharged — payment/auth context the annotations cannot convey. The classification thresholds (+0.5 / -0.5 / neutral) also tell the agent how values are derived.

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 core definition, then thresholds/freshness, then pricing. No filler; the parenthetical threshold explanation is compact and earns its place. Slightly dense but not padded.

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, return-shape detail is unnecessary, and the description covers definition, classification rule, freshness cadence and payment mechanics. Nothing an agent needs to call it correctly is missing, though a hint about typical use (e.g., agricultural/energy demand forecasting) would round it out.

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 single 'seasons' parameter is fully documented in the schema with its range and default. The description adds nothing about the parameter, so the baseline 3 applies rather than anything higher.

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 names the exact dataset (NOAA CPC Oceanic Nino Index), the measurement (3-month running SST anomaly in Nino 3.4) and the derived label logic, which clearly separates it from every sibling tool in the list. It lacks an explicit action verb ('retrieve/fetch'), so the operation is inferred rather than stated, keeping it just below the top mark.

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?

Usage is implied by the domain — an agent would call this when it needs ENSO state — but the description never says when to use it versus alternatives, nor any exclusions or prerequisites. The only implicit guidance is the 'updated monthly' note, which hints the data is not real-time.

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