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

Adds meaningful behavior beyond the annotations: partial-update semantics ('Only the fields you pass change'), an ownership requirement, and two hard constraints (immutable scope, uneditable platform-scoped events). The destructiveHint already flags risk, but the description usefully specifies what is and isn't mutable.

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?

Four tight sentences, front-loaded with what is edited, then the partial-update rule, then the two constraints. No filler and each sentence carries actionable information.

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 mutation tool with annotations and an output schema, the description covers mutation semantics, ownership, and immutability constraints well. Return values are handled by the output schema, so the only minor gap is the required annotationId not being explicitly addressed.

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 only 17%, so the description carries much of the burden, and it does name all five optional editable fields (date, label, description, category, colour) mapping to eventDate/label/description/category/color. However it adds no format or syntax detail beyond the schema's own property names, and annotationId is never discussed, so it only partly compensates.

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+resource ('Edits a chart annotation') and enumerates the editable fields (date, label, description, category, colour). It also distinguishes itself from siblings by naming the delete+create route for scope changes, so an agent can place it against create_annotation/delete_annotation.

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?

Provides clear context (editing an owned annotation) and explicit exclusions with an alternative: scope cannot change, 'delete it and create a new one instead', and platform-scoped system events cannot be edited. It stops short of a general when-to-use vs create_annotation routing statement, but the alternatives for the edge cases are concrete.

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