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

Annotations already declare readOnlyHint/openWorldHint/destructiveHint, and the description adds meaningful behavior beyond them: the API-key requirement, currency-dependent subscription errors, and the empty-result meaning. There is no contradiction with the annotations.

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 description is three tight sentences: purpose first, then authentication/empty-result behavior, then the currency access rule. Every sentence adds distinct information and 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?

The description covers purpose, authentication, error behavior, and empty-result semantics, and the output schema covers return values. However, for a tool with nine parameters and zero schema description coverage, the optional filter semantics (dates, measure, source, issuer, offset/limit) remain unexplained, leaving real gaps for correct invocation.

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% for 9 parameters, and the description does not compensate. It never explains limit, offset, issuer, source, measure, start_date, end_date, or instrument_id. Mentions of issuer, instrument, maturity, curve type, and source precision are framed as output preservation, not input parameter semantics, and currency is only discussed in access rules.

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 opens with a specific verb and resource: 'Read persisted official financial price observations,' then enumerates the covered instrument categories (government yield curves, individual securities, overnight benchmarks, reference prices). This clearly identifies what the tool does and sets it apart from general price/rate tools by emphasizing official, persisted observations.

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 provides clear operational context: an API key is required, USD works without a key, other currencies return subscription_required with a subscribe link, and empty results mean no stored observations exist. However, it does not explicitly say when to use this tool versus sibling alternatives such as rate_curve or fx_intraday_reference_rates.

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