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

Annotations cover the safety profile (destructiveHint=false, idempotentHint=true), and the description adds genuinely new behavior: watching triggers outbound email to the user, and watch permission equals issue read permission. The only gap is what a repeat call returns when the user is already a watcher, which is left to the idempotent hint.

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?

The first line is a verbatim copy of the title field, including the '(idempotent; spec D92)' spec reference, and idempotence is then restated twice more. The core guidance is front-loaded and short, but roughly a third of the text is redundant with structured fields.

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 two-parameter, non-destructive mutation with full schema coverage, annotations, and no output schema, the description covers the decisions an agent must make: permission, side effect, and urgency. Only the already-watching response case is unstated.

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?

Both parameters are fully documented in the schema (100% coverage) with patterns and examples, so the baseline of 3 applies. The description adds no parameter-level meaning such as whether `project_key` must match the issue's actual project.

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?

Specific verb+resource ('Watch the issue yourself'), and the description clarifies the watch is scoped to the token's user, which distinguishes it from tools like `list_watchers`. It never names `unwatch_issue`, so the reverse operation must be inferred from naming alone, but the action itself is unambiguous.

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?

Explicit when-to-use gate: 'Only when the user asks — watching sends them emails' gives the agent a precise condition, plus permission ('Anyone who can read the issue may watch it') and an alternative path ('Adding a comment also makes you a watcher'). All three of context, prerequisite, and alternative are present.

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