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

Goes well beyond the annotations (destructiveHint/true, idempotentHint/true) by explaining the non-obvious replace semantics: it reads the current contact and sends it back whole, preserving lists, opt-in, blocked state and attributes while applying only the caller's changes. That is exactly the context an agent needs to not fear clobbering unmentioned fields on a destructive-looking tool.

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 sentences with zero filler, front-loading the mutation type and target before the behavioral caveat and the endpoint. Nothing repeats the title or annotations verbatim.

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 six-parameter write tool with no output schema and only partial parameter descriptions, the read-modify-write explanation covers the highest-risk unknown. It is slightly thin on the request shape (which fields pair with which, required contact_id) and says nothing about the response.

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 50% and the description only names the three loosely-described fields (name, email, mobile). It adds nothing about contact_id being required, the mobile/country pairing constraint, or first_name vs last_name, leaving the schema to carry the rest.

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?

Opens with an explicit verb-and-mutation marker ("WRITE: change a contact's name, email or mobile") naming the exact resource and fields affected. It also names the concrete endpoint, so an agent can distinguish it from sakari_create_contact and sakari_get_contact without opening schemas.

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?

The "WRITE" prefix and the required contact_id context make it clear this is for modifying an existing contact rather than creating one. It does not explicitly name an alternative for creating or reading a contact, so the exclusions are only implied.

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