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

Annotations already communicate idempotentHint=true and destructiveHint=false, so the description does not need to restate safety behavior. It adds the scoping detail that only notifications from signals.openings.list are accepted, matching the annotations without contradiction.

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, front-loaded sentence contains the verb, resource, source, and scope with no filler. Every phrase earns its place.

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 one-parameter, idempotent, non-destructive mutation with full schema coverage and an output schema, the description plus annotations leave no material gap. An agent can determine the input source and effect.

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% and notification_id is already described as the id from signals.openings.list. The description repeats this relationship but adds no new parameter-level detail, so the 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?

Description states a specific action ('Mark ... as read'), a precise resource ('one opening notification'), and its origin ('returned by signals.openings.list'). This distinguishes it from the sibling signals.openings.mark_all_read without needing to inspect 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?

The description implies the proper workflow: call signals.openings.list first, then mark a returned notification. It does not explicitly contrast with mark_all_read or state when not to use this tool, but the singular 'one' plus the referenced list tool provides a clear usage context.

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