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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=true, so the safety profile is covered. The description adds value beyond that with the manage-token authorization requirement and the concrete endpoint (POST /sites/{site_id}/milestones/{milestone_id}); it does not explain what the overwrite destroys, but the remaining gap is modest.

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?

One compact sentence front-loads the action and scope, followed by the two facts an invoker most needs (required fields, auth) and the endpoint. No filler.

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 four-parameter mutation tool with no output schema, the description covers action, scope, required inputs, auth, and transport. Idempotency and destructive semantics are delegated to annotations, which is acceptable, though failure modes (invalid milestone id, insufficient token) are left to the API.

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%, so all four parameters are already documented in the schema, including the id sources (fathom_list_sites, fathom_list_milestones). The description only restates that name and milestone_date are required, a fact the schema's required array already carries, so baseline 3 applies.

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 precise verb+resource ('Rename or re-date a milestone') and sharply bounds the scope to two mutable fields, which distinguishes it from fathom_create_milestone, fathom_delete_milestone, and fathom_get_milestone without needing to name them.

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 real invocation context: both name and milestone_date are mandatory, and a manage token is required for the site. It stops short of naming alternatives (e.g. fathom_get_milestone to first read the existing date), so it is clear context without explicit when-not guidance.

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