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

With no annotations, the description carries the full burden. It discloses the key behavioral trait: omitted fields are left as-is, and passing an empty string clears a field (vs. omitting which keeps current value). This is critical for correct usage and goes beyond what the schema provides. It does not mention error behavior or auth, but the core mutation semantics are well explained.

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 two sentences with no filler. It front-loads the purpose and immediately follows with the essential behavioral note. Every word earns its place; no redundant information.

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 simple patch operation with 7 parameters and no output schema, the description covers the main pitfall (omission vs clearing). It does not mention error handling or response format, but these are often assumed for such tools. Given the low schema coverage and absence of annotations, it provides sufficient context for correct invocation, though it could optionally note what happens if the id is invalid.

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 14% (only 'id' is described). The description compensates by explaining the general rule for all fields: only include fields to change, and empty string clears. This provides crucial meaning beyond the schema's bare type declarations. It does not individually describe each parameter, but the names are self-explanatory and the patch semantics apply uniformly.

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 ('Patch'), a resource ('an existing contact'), and clarifies the partial-update semantics. It clearly distinguishes from contacts_create, contacts_delete, and contacts_get/list by indicating modification of an existing record.

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 purpose is clear: this tool updates an existing contact. It provides clear context for when to use it (to modify a contact) but does not explicitly mention alternatives or exclusions. The description does not say 'use this instead of create' but the verb 'patch' makes that implicit. No direct comparison to sibling tools, but the context is unambiguous.

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