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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds real value beyond that by previewing the response content (line type, validity, opt-in and blocked state) in the absence of an output schema. It does not mention auth scopes, rate limits, or not-found 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 clauses with zero filler; the 'one contact by id' scope and the returned fields are both front-loaded before the endpoint reference.

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 one-parameter read tool with full annotation coverage, this is nearly complete – the field list substitutes for the missing output schema. Only error/nonexistent-id behavior is unaddressed.

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?

Single parameter with 100% schema description coverage ('Sakari contact id.'), so the schema already carries the semantics. The description only reinforces 'by id' and adds no format, sourcing, or lookup guidance beyond the schema.

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 retrieval action ('One contact by id') and enumerates the concrete fields returned (name, mobile with validity/line type, email, lists, attributes, opt-in/blocked). The singular 'by id' implicitly separates it from sakari_list_contacts, but no sibling is named explicitly.

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 only implied: an agent can infer it should call this when it already has a contact id and use sakari_list_contacts otherwise. There is no explicit when-to-use, prerequisite, or fallback guidance, and no mention of what happens if the id is unknown.

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