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

Annotations already establish readOnly, idempotent, and closed-world, so the bar is lower. The description adds genuine behavioral context beyond them: the auth condition ('no API key needed') and the shape of each returned entry (field path, unit, source). It omits pagination or ordering behavior, but for a small static catalog that is a minor gap.

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 compact sentences with no filler. The content enumeration is front-loaded and the access constraint is appended rather than buried, so every clause earns its place.

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?

There is no output schema, so the description must carry the return contract, and it does: list of subjects each carrying field path, unit, and source. No input parameters need explaining. Only the exact container/format (array vs. object, sorting) is left unspecified, which is minor for a simple catalog endpoint.

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 zero parameters, so the schema baseline of 4 applies. There is nothing for the description to document beyond confirming the tool is unfiltered and takes no arguments.

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 concrete resource (every queryable subject: Treasury tenors/spreads, FX pairs, crypto assets, aggregates) and specifies the per-item payload (JSON field path, unit, source). It is clearly a catalog/discovery tool, distinct in kind from the brief-fetching siblings, but it never explicitly names or contrasts with those siblings.

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?

Usage is only implied: an agent can infer this is the lookup you call to discover valid subjects/field paths before querying. There is no explicit when-to-use statement, no exclusions, and no routing against get_brief_by_date, get_latest_brief, or get_sample. 'Open, no API key needed' is an access note, not usage guidance.

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