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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=false), so the description's job is lighter. It adds real value by disclosing the default account-level visibility, the siteUrl scoping behavior, and the reserved platform-wide scope — none of which the annotations convey.

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 scope semantics, then the exclusion. Every sentence carries information and none is 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?

An output schema exists, so return values need no explanation, and the safety profile is covered by annotations. The description is complete enough for an agent to call the tool correctly, with the main residual gap being its silence on the non-required fields.

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 only 43% across 7 parameters, so the description is expected to compensate, but it only touches siteUrl — and largely repeats that parameter's own schema description. Terms like label, color, category, and description receive no clarification the schema doesn't already imply, leaving the low-coverage params underspecified.

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 ('Adds a chart annotation'), which is unambiguous against siblings like list_annotations, update_annotation, and delete_annotation. It does not, however, explicitly name a sibling or contrast with one, so it stops short of a 5.

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?

Gives clear context: account scope is the default, pass siteUrl to narrow to a property, and platform-wide annotations are not creatable here. That last clause is a genuine when-not condition. It stops short of a 5 because it never names an alternative tool or workflow.

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