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

Annotations already convey that this is a non-read-only, non-idempotent, and non-destructive operation. The description adds conceptual context about grouping work toward a date but does not disclose further behavioral details such as duplicate behavior, permissions, or required project existence.

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?

A single, compact sentence that front-loads the core action and purpose. There is no wasted wording or redundancy, apart from the title, which is fine.

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 simple create operation with schema-documented parameters and no output schema, the description is largely sufficient. It could be slightly more complete by referencing the targetDate parameter or noting that the named project must already exist, but these are minor gaps.

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 50%, with project and targetDate already documented. The description helps clarify that 'name' is the milestone's name and that the milestone belongs to a project, but it does not add much meaning beyond the schema for the remaining parameters.

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 states a specific action ('Add') and resource ('a milestone to a project') and explains the purpose ('so work can be grouped towards a date'). This clearly distinguishes it from sibling tools like update_milestone, delete_milestone, and reorder_milestones.

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?

The usage is implied through the verb 'Add': this tool is for creating a milestone in a project. However, there is no explicit guidance about when not to use it or how it compares with related tools such as update_milestone or reorder_milestones.

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