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

Annotations already declare readOnly=false, idempotent=false, destructive=false, so the safety profile is covered. The description adds genuine context beyond that: notes are 'visible to everyone in the account who sees the call', the specific 404 retry path, and the underlying PUT endpoint. It does not address permission requirements or duplicate-note behavior on retry, but the added operational detail is substantive.

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 WRITE: marker, no filler. Every clause carries information: operation scope, visibility, identifier fallback, and endpoint.

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 two-parameter mutation with full schema coverage, functional annotations, and no output schema, the description supplies what an agent needs: what it writes, who sees it, how to resolve the id, and how to handle a 404. Missing only marginal items such as whether multiple notes can coexist or what a success response looks like.

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 coverage is 100%, so the baseline is 3. The description earns above baseline by telling the agent that `id` is the primary identifier and that the record's `callId` should be tried when Rinkel answers 404 — a resolution rule the schema does not state.

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 opens with a specific verb and resource ('add a note to a call record') and leads with a WRITE: marker, making the operation type immediately clear. It implicitly separates itself from update_call_note and delete_call_note, though it never names them 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?

Usage is implied by the note-adding framing, and there is useful edge-case guidance for the 404 path (retry with the record's `callId`). However, no sibling alternatives are named and there is no explicit statement of when NOT to use this versus update_call_note, so a substantial part of the guidance burden is left to inference.

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