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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered without the description's help. The description adds domain semantics (first-class entity with dueDate + completed) but nothing on missing-ID behavior or return shape, so it is a modest add-on against an already-strong annotation set.

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 purpose front-loaded and the disambiguating clause following immediately. Nothing could be cut without losing 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 read-only single-entity fetch with a one-field schema and rich read-only annotations, the description is nearly sufficient; it even flags two returned fields. It claims 'Full detail' without indicating the return surface, and no output schema exists to carry that, leaving a small gap.

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 0% and the single milestoneId parameter has no documented format beyond being a required string. The description's 'one Milestone row' frames it as a singular identifier lookup, which is weakly helpful, but it adds no syntax or source-of-value detail to compensate for the empty schema description.

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?

Names a specific verb+resource ('Full detail on one Milestone row') and explodes a real ambiguity by contrasting with Task.isMilestone, noting Milestone is a first-class entity with dueDate + completed. It does not explicitly contrast with the actual sibling list_milestones, so a 4 rather than 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?

Usage is only implied: the tool fetches one row, so an agent can infer it is the singular counterpart to list_milestones. There is no explicit when-to-use or when-not-to-use statement, however, so guidance stays at minimum-viable.

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