create_contact_property

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

With no annotations, the description carries the full burden. It discloses a non-obvious behavioral trait: idempotency on key, returning the existing property with 'already_existed: true' instead of erroring. It also names the POST endpoint. It doesn't mention permissions or the normal success response, but the idempotency disclosure is substantial and valuable.

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 compact sentences deliver the purpose, endpoint, type constraint, and idempotency behavior without redundancy. The most important information is front-loaded, and every clause earns its place.

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 create tool with no output schema, the description covers the core action, the type enum, and the key edge case of duplicate keys. It omits the normal success return shape and authentication requirements, but the idempotency explanation addresses the most critical ambiguity an agent would face.

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 100%, so the baseline is 3. The description adds semantic meaning to 'key' by establishing it as the idempotency identity, which goes beyond the schema's 'Canonical merge-tag key' phrasing. Other parameters remain adequately covered by the 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?

States a specific verb ('Create') and resource ('custom contact property / merge tag'), and includes the HTTP endpoint. This clearly distinguishes it from siblings like update_contact_property, delete_contact_property, get_contact_property, and list_contact_properties without needing to inspect their 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 description implies usage for creating or ensuring a property exists, and the idempotency behavior suggests it can be used safely when a key may already exist. However, it does not explicitly route to alternatives like update_contact_property when modification is intended, nor give any when-not-to-use guidance.

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