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

With annotations already covering the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=true), the description adds substantial behavioral context: it is free, fictional, opens/scans a sample letter, delivers real events, proves only transport receipt and keyword match (never agent processing), requires webhook.manage, uses bounded control plane and tenant/agent/Live-Sandbox authorization, and specifies idempotency key reuse. This far exceeds the annotation coverage.

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 front-loaded with the core action and keeps every sentence relevant: scope, limits, permissions, idempotency, and docs link. It is dense but not redundant; a slightly leaner phrasing could still convey the same information, but the length is justified by the tool's complexity.

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?

Given the tool's complexity (a test that mutates webhook delivery state), the presence of annotations, and an output schema, the description is complete. It covers what the tool does, what it does not do, auth requirements, idempotency behavior, and how to interpret success, leaving no critical gap for an agent to call it correctly.

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 adds a meaningful nuance beyond the schema's idempotency_key description by specifying 'Reuse the exact idempotency_key and input after an uncertain mutation,' clarifying when reuse is appropriate. It also ties expected_revision to concurrent-edit safety, though that is largely echoed in 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 states a specific verb and resource ('Run the Sample test' on a webhook endpoint) and distinguishes itself from the generic sibling test_webhook_endpoint by naming the 'Sample' test and describing the exact events delivered (inbound.pages_ready / inbound.keywords_matched). An agent can tell what this tool does without opening any other 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 gives some contextual guidance ('Reuse the exact idempotency_key and input after an uncertain mutation') and prerequisites ('Requires webhook.manage'), but it never explicitly says when to choose this tool over test_webhook_endpoint or replay_webhook_delivery. Usage is implied by the name and context rather than stated with alternatives or exclusions.

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