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

Annotations already establish readOnly, idempotent, open-world, and non-destructive, so the safety profile is covered. The description adds genuinely useful behavior beyond that: it returns latest value plus last-change date plus history, it normalizes plain names instead of SDMX keys, it caps at 20 series, and it states the price model ($0.002 per series). It does not mention rate limits, error behavior for unknown series names, or what an empty result looks like.

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 first sentence front-loads what you get back, the second enumerates coverage, and the price line is short and actionable. The phrase about being built for AI agents and anyone needing a quick sourced number is mild marketing filler that does not help an agent decide anything, but the rest earns its space.

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?

With seven optional parameters and no output schema, the description does carry the burden of describing return values, and it does so concretely (latest value, when it last changed, the change, recent history). The notable gap is that `catalogue` mode is effectively undocumented in both schema and description, so an agent has no idea what discovery output it would get.

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%, so all seven parameters including date windows, `last`, `frequency`, and `rawSeriesKey` are already documented in the schema. The description reinforces the plain-name convention and the no-SDMX-keys benefit, and shows inline examples like `ecb_deposit_rate` and `eur_fx:USD`. It adds little beyond the schema and never explains the `catalogue` mode value, which the schema also leaves undocumented.

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: return the latest value, last-change date, change, and recent history for euro-area rates. It enumerates the covered domains (ECB policy rates, euro reference FX, 60STR, sovereign yields, Eurostat HICP) and states the key differentiator, no SDMX series keys required. No sibling tool covers interest rates or inflation, so an agent can place it accurately.

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 framing (ask by plain name, quick sourced number, 20 series per run, cost per series) but never states when to prefer it over alternatives or when not to call it. The schema exposes a `catalogue` mode and a `rawSeriesKey` fallback, yet the description says nothing about when an agent should use catalogue discovery or escape to raw keys, which are the real routing decisions for this tool.

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