Reject a pending send

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

Annotations already signal readOnlyHint=false and idempotentHint=true, so the description's main contribution is explaining the real-world effect: the send 'is never delivered'. It also discloses process constraints — only 'reject' is accepted and approval requires an owner or admin in a browser session. This is meaningful context beyond the structured annotations, though it stops short of stating whether the rejection can be undone.

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 description is two tight sentences with no filler. The primary action and consequence are front-loaded, and the second sentence covers the critical limitation (no approval via MCP) without digressing into schema details or sibling comparisons. Every clause 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 simple mutation with 3 parameters and no output schema, the description is largely sufficient: it clarifies what this tool does, what it cannot do, and how the only decision value behaves. It does not describe the success response or what happens after rejection, but the core decision an agent needs to make — when and how to call it — is fully covered.

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 input schema fully documents approval_id, decision, and note. The description adds useful emphasis that decision accepts only 'reject' and explains why approving is not available, but this largely mirrors the schema's own parameter-level description. Thus the description adds only marginal semantic value beyond the schema.

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', and adds the key consequence 'so it is never delivered'. It also distinguishes itself from approval actions by declaring that approving is not available over MCP. This makes the tool's unique role unambiguous against siblings like approval_review and approval_schedule.

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 gives explicit usage context: use this when a send is pending human approval and needs to be rejected. It also gives a clear when-not: approval is deliberately not offered here and requires a signed-in browser session at the review_url. This routes the agent away from misuse even without naming a sibling tool.

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