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

Annotations already declare readOnly, idempotent and openWorld=false, so the safety profile is covered; the description adds genuinely new behavior: the 49-country coverage envelope, the returned fields (month of latest decision and previous rate where changed), and a paid-call requirement of $0.002 USDC per call via x402 on Base mainnet. That payment disclosure is materially important for an agent and is not available from any structured field. Gaps remain around data freshness/refresh cadence and failure behavior.

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?

Front-loaded with the resource and coverage, then filtering, then use cases, then price — a sensible order with no filler sentences. The bank-name enumeration is somewhat long but earns its place by establishing coverage breadth and differentiating the CFA-zone groupings.

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 single-optional-parameter lookup with no output schema, the description supplies the essentials: what data, what coverage, which fields, how to filter, and what it costs. It does not state update frequency or data-source latency, which matters for a rates tool used in pricing decisions, so it stops short of fully complete.

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 100% for the single optional 'country' parameter, and the description's 'Filter by ISO country codes' restates rather than extends it. No format subtleties (spacing, case sensitivity, how multiple codes serialize, behavior on an unknown code) are added, so the baseline 3 applies.

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 — central bank policy interest rates for 49 African countries — and enumerates concrete institutions (SARB repo, CBN MPR, CBR, BCEAO, BEAC), which tells an agent exactly what data comes back. It implicitly bounds itself against the South Africa-only sibling za_sarb_rates via the '49 countries' scope, but never names that sibling, so differentiation is inferential rather than explicit.

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 offers downstream use cases ('loan pricing, FX and macro context') and the filtering mechanism ('Filter by ISO country codes'), which implies when it is appropriate. There is no when-not guidance and no routing to alternatives such as za_sarb_rates for a single-country SARB rate or exchange_rates for currency quotes, leaving overlap resolution to the agent.

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