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

Annotations cover the safety profile (not read-only, not destructive, not idempotent), and the description adds non-obvious behavior: the note is authored by the API key holder and appears on the dashboard timeline. It doesn't state rate limits or whether notes can be deleted, but the signing behavior is genuinely useful context beyond the annotations.

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, front-loaded with the purpose and followed by behavioral context. No filler, though the restated title as the first line is mildly redundant.

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 three-parameter, non-destructive mutation with full schema coverage and annotations, the description is adequate. However, it omits usage guidance relative to siblings and does not mention any response shape, which would help since there is no output schema.

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%, with detailed error semantics for each parameter (422, 404, 403). The description adds nothing about parameters, so the baseline 3 applies when the schema fully documents them.

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 a specific verb (Add) and resource (note to a contact), clearly distinct from siblings like update_contact_note or list_contact_notes. It doesn't explicitly differentiate itself from those siblings, but the creation semantics are unambiguous.

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?

No when-to-use guidance, no mention of alternatives like list_contact_notes or update_contact_note, and no note about whether this can be repeated. The agent must infer applicability from the name alone.

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