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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=false, so safety is largely covered. The description adds a genuine behavioral fact not in the annotations: the required milestone.create permission on the target project. It omits return shape, but that is a minor gap against annotation coverage.

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, zero filler, with the core action and its scope front-loaded before the permission caveat. Nothing here is redundant with the name or the annotations.

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 4-parameter mutation tool with no output schema, the description covers purpose and authorization but says nothing about what is returned (e.g., a milestone id) or duplicate/error behavior beyond what the schema's idempotencyKey note supplies. Adequate but with visible 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 coverage is 75%, so most parameters carry their own descriptions (title length bounds, ISO date format, and a detailed idempotencyKey contract). The description only indirectly gestures at projectId via "on one project" and adds no semantics beyond the schema, so baseline 3 is appropriate.

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 gives a specific verb+resource ("Create a milestone") plus scope ("on one project") and a semantic differentiator ("zero-duration marker for key dates") that separates it from sibling create_task or create_epic. An agent can tell what this tool produces without opening the schema.

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?

It states a hard precondition (caller must hold milestone.create on the project), which tells the agent when the call will be permitted. However, it offers no guidance on when to prefer this over siblings like update_milestone, propose_milestone_completion, or list_milestones, and no exclusions or alternative routing.

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