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

Annotations supply only destructiveHint=true and a title, so the description carries most of the burden. It usefully discloses that no outbound call is dialed and gives the backing endpoint (POST /v1/calls), but it does not explain the write semantics, permission requirements (the schema notes userId is admin-only), or what is created/returned. Adequate but thin for a mutation 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?

Three short sentences, front-loaded with the core action, then the scope exclusion, then the API mapping. No filler and nothing buried.

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 mutation tool with no output schema and minimal annotations, the description covers the what and the not-what but omits return behavior, permission constraints, and any guidance on the optional fields (recordingUrl, fromNumber/toNumber, duration). It is sufficient to start but not to call confidently.

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?

Ten parameters at 60% schema description coverage, and the description adds essentially nothing about them beyond 'with its outcome,' which merely gestures at the outcome field already enumerated in the schema. Required fields (personId, phone, isIncoming) and the admin-only userId restriction are left entirely to 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?

The description gives a specific verb and resource ('Record a phone call ... with its outcome') and adds a scope qualifier ('made or received outside FUB') plus the negative constraint 'Does not place a call.' It clarifies the operation well, though it never names the sibling it is meant to be distinguished from (e.g. fub_add_note or 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?

'Record a phone call made or received outside FUB' states when to use it, and 'Does not place a call' rules out a plausible but wrong interpretation. However, no alternative tool is named for the case where the call is placed by the system or when the user wants to attach a note instead.

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