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

Annotations already declare readOnlyHint, openWorldHint and destructiveHint=false, so safety is covered structurally. The description adds only the field list and the raw endpoint name; it says nothing about result limits or API quota despite the schema's warning that every call counts against an hourly quota.

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?

Three short clauses, front-loaded with the resource and followed by returned fields and filters. Zero padding, though the 'contact.get.' fragment is noise an agent does not need.

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 read-only listing tool with no output schema, the description supplies what the schema cannot: what each contact record contains (name, position, e-mail, phone). Pagination and quota exist in the schema, so nothing critical 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 83%, so the schema already documents term, limit, offset and the id filters precisely. The description restates three of six parameters ('customer, search term or contact id') without new syntax or behavior, leaving customer_number, limit and offset entirely to the schema. Baseline 3 applies.

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 a specific verb and resource ('List contact persons of customers') and enumerates the returned fields, which cleanly separates it from fastbill_list_customers and fastbill_get_customer. The trailing 'contact.get' is an API endpoint hint rather than added clarity.

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 names the available filters (customer, search term, contact id), which implies how to narrow results, but it never says when to choose this over fastbill_list_customers or fastbill_get_customer, nor when not to use it. Usage is inferable but not guided.

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