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

Annotations already provide idempotentHint, readOnlyHint, and destructiveHint, and the description adds meaningful behavior: the effect ('never delivered'), the accepted decision value ('only reject'), and the auth limitation for approvals. No contradiction with annotations exists.

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 tight sentences with the core action and outcome front-loaded. The second sentence adds the constraint and alternative without excess. Every phrase contributes.

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 simple, well-annotated mutation tool with an output schema, the description covers the action, the only accepted decision, and the alternative for approving. It does not explicitly state the post-rejection state of the approval, but the schema and output schema fill the remaining context.

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 description coverage is 100%, so the baseline is 3. The description restates the decision constraint that already appears in the schema ('decision accepts only reject') without adding new parameter context such as where approval_id comes from or how note is used.

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 opens with a specific verb and resource: 'Reject a send that is waiting for human approval, so it is never delivered.' It states the outcome explicitly and immediately distinguishes itself from approval actions by noting 'Approving is deliberately not available over MCP.' The title reinforces the scope.

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 clearly establishes when to use the tool (to reject a pending approval) and explicitly warns when not to (approving requires a signed-in browser session with owner/admin). It does not name a sibling MCP tool as an alternative, but the boundary between this tool and the browser review flow is explicit.

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