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

readOnlyHint already declares this a safe read, so the description doesn't need to restate safety. It adds the useful detail that records carry outcome/direction/duration and cites the backing endpoint, but says nothing about pagination behavior or result volume, which matters for a list endpoint with limit/offset.

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 short sentences, resource-first, with no filler. The endpoint reference is compact and useful; nothing is wasted, though the sentence fragment style is minimal.

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 read-only, six-parameter, no-required list endpoint with full schema documentation and no output schema, the description covers what the tool returns and how to filter. Only pagination behavior is left implicit, which the schema's limit/offset partially handle.

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 every parameter is already documented and the baseline is 3. The description's 'filter by person or number' loosely maps to phone/personId/toNumber/fromNumber but adds no syntax or format detail beyond 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?

Names the resource precisely ('Logged phone calls') and the fields returned (outcome, direction, duration), plus binder of the endpoint. Distinguishes itself from the write sibling fub_log_call, though it never names an alternative explicitly.

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?

'Filter by person or number' implies how to narrow results but gives no when-to-use guidance versus siblings like fub_list_text_messages, fub_list_events, or fub_log_call. Usage is inferable but not stated.

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