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

Annotations supply only destructiveHint=true, so the description must carry the rest. It discloses the mutation nature via 'Record' and the POST endpoint, plus the non-dialing behavior, but says nothing about side effects (timeline/activity entries), permissions, or whether an existing call can be overwritten — leaving the destructiveHint unexplained.

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?

Three tight sentences with zero filler, front-loading the purpose, then the clarification, then the endpoint reference. Nothing needs to be trimmed or moved.

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 10-parameter creation tool with no output schema and sparse annotations, the description covers purpose and the key non-behavior but omits side effects, the significance of destructiveHint, and any guidance on the partially documented parameter set.

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 60% across 10 parameters, so the schema does much of the work, and the description adds only 'with its outcome' as a nod to the outcome enum. It gives no guidance on the required triple (personId, phone, isIncoming) or on the undocumented fields like toNumber/fromNumber.

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 ('Record a phone call made or received outside FUB, with its outcome') and immediately disambiguates the most likely confusion by saying 'Does not place a call.' It also names the backing endpoint (POST /v1/calls), which pins it as the write-side counterpart to fub_list_calls.

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 negative clause 'Does not place a call' usefully rules out a misread (dialing), and 'outside FUB' scopes the use case to offline calls. However, it never states prerequisites (e.g., the person must already exist) or points to a sibling for anything adjacent, so usage is only implied.

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