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

Annotations already declare readOnly=true, destructive=false and openWorld=true, so safety is covered. The description goes further by disclosing the return payload fields and the HTTP endpoint — useful since there is no output schema. It stops short of pagination, ordering, or empty-result behavior.

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 the resource and its fields front-loaded, then the endpoint. Nothing is redundant, though the parenthetical field list is slightly dense for a single sentence.

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 trivial one-parameter read tool with annotations covering the safety profile, the description supplies the resource scope and the shape of the return data, which is the main thing missing given no output schema. Minor gaps remain around result ordering/pagination and behavior for an unknown client id.

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 single parameter's schema description coverage is 100% ('Bilflo client id.', integer > 0), so the schema does the work. The description corroborates scope ('of one client') and the path placeholder {clientId}, but adds no format, sourcing, or lookup guidance beyond that.

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 the exact resource (contacts of one client) and even enumerates the returned fields (name, title, phone, email, active flag), plus the underlying endpoint. It does not explicitly contrast itself with the adjacent list_client_addresses / list_client_agreements siblings, but the resource noun is distinct enough that an agent can distinguish them.

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?

There is no when-to-use guidance, no stated preconditions (e.g. needing a valid client id or that it returns an empty list for clients without contacts), and no mention of alternatives. The only implicit signal is 'of one client', which the schema already conveys.

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