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

Goes well past the annotations (readOnly/idempotent/closed-world) by describing what is returned — configured overnight_target and bank_rate definitions, collection status, coverage since 2010, latest observations, citation and freshness — and adds a critical caveat that a source_unavailable_or_stale status means configured definitions do not prove data availability. Also discloses provenance limits ('not independently verified') that the structured fields cannot convey.

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-loads the core routing purpose and the no-argument call, then layers returns, usage, and caveats in a logical order. It is dense for a zero-param tool, but nearly every clause (scope exclusions, staleness caveat, provenance) carries distinct value, so little is wasted.

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?

Despite an output schema already existing, the description covers the essentials an agent needs: purpose, no-arg invocation, what comes back, the follow-up route to get_interest_rates, a staleness pitfall, and scope boundaries (Canada only, not retail/real-time). Nothing material is missing.

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?

Zero parameters, so the baseline is 4, and the description correctly reinforces this with 'Call with no arguments.' The schema at 100% coverage already documents the empty object, so no further parameter detail is needed.

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 verb and resource ('Discover the two Canadian policy-rate series') and clearly frames the tool as a directory that precedes get_interest_rates. An agent can distinguish it from the sibling get_interest_rates without opening 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?

Explicitly says when to use it ('before get_interest_rates when the series key or year coverage is unknown'), how to call it ('no arguments'), and when to skip it ('skip this directory if those inputs are known'). The routing condition and exclusion are both stated, leaving nothing to inference.

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