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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint, so safety is covered. The description adds that the payload includes customer personal data and that `with` pulls in related addresses/accounts, but says nothing about error behavior for missing IDs, auth, or response shape.

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 with the primary action front-loaded; the parenthetical about documented relations is slightly wordy but earns its place by clarifying which relations apply. No filler sentences.

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 two-parameter read tool with no output schema, the description covers purpose and relation expansion, but leaves return shape, not-found behavior, and the contact_id domain to inference. Adequate, not complete.

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 description coverage is 0%, so the description carries real weight here and it does explain the `with` parameter's semantics (addresses or accounts, single-contact route relations). However it never describes contact_id beyond 'by id', nor the maxItems=2 cap, so the two undocumented parameters are only half compensated for.

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 ('Get one contact by id') with scope made explicit by 'one' and 'customer personal data', which distinguishes it from the sibling plentymarkets_list_contacts without needing 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 only implied: the reader infers this is for single-contact retrieval and the list tool is for enumeration. There is no explicit 'use this when…' statement, no mention of when to prefer list_contacts, and no prerequisites noted.

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