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

Annotations only declare readOnlyHint=true, so the description carries the rest and does: it discloses the paging mechanism (pass next_offset as offset), the filterable surface, and the HTTP verb/path. It does not mention auth requirements or rate limits, but for a safe read list it adds genuine operational context beyond the annotation.

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 tightly packed sentences, front-loaded with purpose, then filters, then paging, then endpoint. No filler and no repetition of schema-level defaults.

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 four-parameter list tool with no output schema, the description covers the filtering surface, pagination, and endpoint. The remaining gap is return shape, but next_offset implicitly signals the paged-envelope format, so an agent has enough to invoke it correctly.

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 100%, so baseline is 3, but the schema itself defers to the description for the valid filter field names ('the list tool's description names the valid ones'). The description supplies that exact list, making it materially additive rather than redundant.

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 contacts') and immediately resolves a naming ambiguity that would otherwise confuse an agent: 'the people at customers; the API calls them users.' It also names the backing endpoint (GET /user), so the tool is unambiguously distinct from get_contact and the create/update 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?

Gives concrete usage context: which fields may be filtered, how to page via next_offset, and the parenthetical 'contacts of one customer' for customers.customer_id. It stops short of stating when to prefer get_contact or how to combine filters with other list tools, so it is clear but not exhaustive.

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