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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; the description adds genuinely useful behavior beyond that — the mid-rate (PMI) basis, the SEK-per-1-unit orientation, and the staleness caveat that the returned date may lag today. It stops short of noting error behavior for unsupported currencies.

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 purpose, then return semantics, then the argument spec — a sensible ordering with no filler. The "using the API from Riksbanken" clause is mildly redundant with the following sentence naming Riksbanken again.

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-parameter read tool, the definition covers purpose, rate semantics, publication cadence, date staleness, and argument format; an output schema exists, so return structure needs no further explanation. Nothing an agent needs to invoke it 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?

Schema coverage is 0%, so the description carries the burden and largely does: it specifies the 3-letter ISO 4217 format and gives concrete examples (USD, EUR), which is what an agent needs to call it correctly. Minor gaps remain, such as what happens with unsupported or lowercase codes.

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?

"Fetch the latest exchange rate from some currency to SEK" gives a specific verb (fetch), resource (exchange rate) and direction (X to SEK), plus the data source (Riksbanken). An agent knows exactly what this returns without opening the 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?

Usage is implied rather than stated: the description notes the rate is published on banking days and may be dated earlier than today, which tells the agent this is a latest-only, non-historical read. There is no explicit when-to-use/when-not framing, though no sibling alternatives exist to route away from.

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