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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds real behavioral context beyond that: the data is a live snapshot, access requires no registration, and the funding sign convention is spelled out ('positive = longs pay shorts'), which prevents a very common misinterpretation. 'Data, not advice' also sets expectations about the response's nature.

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?

A single front-loaded sentence with a tight field list, plus two short disclaimers. Every clause carries information; the field enumeration is dense but readable. Slightly more fragmented than ideal, but there is 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?

An output schema exists, so return values need not be explained, yet the description usefully previews the payload anyway. For a no-argument, read-only snapshot tool this is close to complete; only the absence of freshness/refresh semantics and sibling routing keeps it from a 5.

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 tool takes zero parameters, so the baseline is 4 and there is no schema meaning for the description to compensate for. Nothing about argument usage is missing or misleading.

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 resource precisely ('Every Decibel perp market') and enumerates exactly which fields come back: mark price, oracle price, hourly funding in bps, open interest in contracts and USD, and the mark-vs-oracle gap. An agent knows this is a market-snapshot read. It falls short of 5 only because it never contrasts itself with the nearby 'ask_decibel' tool, which is a plausible competitor for market questions.

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 rather than stated: the 'right now' framing signals live data and 'No registration needed' signals it is callable without auth, but there is no explicit when-to-use clause and no named alternative (e.g., use ask_decibel for natural-language market questions). The agent can infer the context but must do the routing itself.

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