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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the external provider and its licensing terms, that no points are consumed, and — most valuably — a specific failure mode: the hub returns privacy_consent_required until the controller accepts the current privacy version, with an explicit warning not to fabricate that acceptance. That is exactly the kind of operational detail the agent cannot infer from structured fields.

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 core purpose is front-loaded in the first sentence and the whole thing is short. The style is fragmented and telegraphic ('Does not spend points and does not accept a URL'), and the license date '2026-09-10' is marginal detail, but no sentence is redundant.

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?

For a one-parameter, no-output-schema tool this covers source, licensing, cost, scope exclusions, and the consent gate that can block a call. The main omission is any hint of the response shape (price fields, timestamps) or other error conditions, which matters somewhat given there is no output schema.

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 0% and the schema only constrains the single 'metal' field to a three-uppercase-letter pattern, so the description has to carry the semantics. It does: it lists gold, silver, platinum, and palladium as the accepted values and clarifies the parameter is not a URL. It does not restate the uppercase ISO-style format, leaving a small gap.

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 a specific verb and resource (one metal quote) plus the exact source (gold-api.com) and enumerates the four supported metals. It also carves out what it is not — 'not an ECB currency rate' — which cleanly separates it from the sibling hub_fx without requiring the agent to open either schema.

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 gives clear negative guidance: not a trading instruction, not an ECB currency rate, does not spend points, does not accept a URL. The currency exclusion implicitly routes the agent to hub_fx for exchange rates, and the points sentence signals this is the free option. It stops short of naming the alternative tool outright, so a 4 rather than a 5.

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