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

Annotations already flag destructiveHint=true, idempotentHint=false and openWorldHint=true, so the safety profile is covered; the description goes further by explaining mutation semantics that matter for a destructive tool — only supplied fields change, empty strings clear values, custom_fields merges per key while null deletes one. It stops short of noting permission requirements or what side effects (e.g. flow triggers) a stage change may cause.

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?

Four short sentences, front-loaded with purpose and then each subsequent sentence carrying a distinct, non-redundant rule. Nothing is padded or repeated.

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 7-parameter mutation tool with a nested object, no output schema and destructive annotations, the description covers the semantics an agent most needs to call it safely. Remaining gaps — behavior on unknown custom_field keys, stage-change side effects, and error conditions — are moderate rather than fatal.

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 a moderate 71%, and the description adds real value by documenting clear-on-empty-string for name, email, phone and notes — the notes parameter has no description in the schema at all. It restates the custom_fields merge/null behavior already present in the schema, and gives no guidance on valid stage transitions.

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 ('Update a contact') plus a scope qualifier ('Partial update') that is meaningful for a PATCH-style operation. It does not, however, distinguish itself from the sibling upsert_contact, which is the one tool an agent could plausibly confuse it with.

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?

No when-to-use or when-not-to-use guidance is given, and no alternative is named despite upsert_contact sitting in the same family. The only guidance is implied by the word 'Update' and the partial-update note, which tells how it behaves rather than when to choose it.

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