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

No annotations are provided, so the description carries full responsibility for disclosing behavior. It only mentions that authentication is required and lists updatable fields. It does not reveal whether fields are merged or fully replaced, what happens if contactId does not exist, what the response format is, or any side effects. For a mutating tool, this is under-disclosed.

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?

The description is compact and front-loaded: a clear one-line purpose, an authentication note, then a direct list of required and optional parameters. It avoids unnecessary detail or repetition, though the optional field list could be shortened by pointing to the schema.

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?

With 13 parameters, no output schema, and no annotations, the description leaves critical questions unanswered: what the return value is, whether this is a partial or full update, how errors are surfaced, and what exact authentication mechanism is required. This is insufficient for an agent to reliably invoke the tool without additional assumptions.

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 only 8% (only sessionKey is described). The description repeats parameter names and marks contactId as required and the rest as optional, but this adds little beyond what the schema's required array already shows. It provides no additional meaning about formats, constraints, or field purposes, so it fails to compensate for the sparse 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?

The description states a specific verb ('Update') and resource ('existing contact's information'), clearly distinguishing it from sibling tools like createContact, deleteContact, getContact, and listContacts. There is no ambiguity about what operation this tool performs.

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 phrase 'existing contact' implies this tool is for modifying contacts that already exist, which provides some usage context. However, it does not explicitly name alternative tools like createContact for new contacts or getContact for retrieval, nor does it explain when to prefer this tool. The authentication requirement is a prerequisite, not routing guidance.

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