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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds genuinely useful behavioral context beyond that: figures are sourced from DefiLlama and each value carries its own source and date, which tells the agent the response is attributed and time-stamped rather than live-updating.

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?

Two sentences, zero filler, with the data inventory front-loaded and the usage triggers following. The middle enumeration is long but every listed item is a selection signal, so density is justified rather than padding.

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 no output schema, the description must describe the return payload, and it does so by enumerating the metrics and noting each has a source and date. Coverage is adequate for a zero-parameter read tool; only the exact response shape (nesting, per-metric units) is left unspecified, which is a minor gap.

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 no parameters, so the schema carries nothing to interpret and the baseline is 4. Nothing in the description contradicts or needs to compensate for the empty input 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?

States a specific resource ('Chain-level Arc numbers') and enumerates exactly what it aggregates: USDC/EURC supply, stablecoins, TVL, volume, apps/projects, index closes, timeline. That scope reliably distinguishes it from the per-entity siblings (arc_app, arc_contract, arc_entity), though it never names a sibling explicitly and the 'index closes and a dated timeline' phrasing partially overlaps arc_indices.

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?

Gives concrete invocation triggers — 'how big is Arc', 'how much USDC is on Arc', 'Arc's TVL or volume' — which map cleanly to real user phrasings. It stops short of any when-not guidance or explicit alternative (e.g. use arc_apps for a project list), so routing is aided but not fully resolved.

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