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

With no annotations provided, the description carries the full burden and does meaningful work: it discloses that the same event id and body are re-sent, and warns that handlers must be idempotent — a genuine side-effect disclosure an agent needs before calling. It omits permissions required, whether the delivery record's state changes after replay, and whether replay can itself fail or be repeated.

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 short sentences, zero waste, with the action and eligibility condition front-loaded and the idempotency caveat immediately after. Nothing could be removed without losing information.

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 mutation with no output schema and no annotations, the description covers purpose, state precondition, and the key risk (duplicate handling via idempotency). It is nearly complete; only post-call effects and permission requirements are left unspecified.

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 the single parameter description already tells the agent to get the id from list_merchant_webhook_deliveries. The description adds no additional meaning about the deliveryId (format, uniqueness, whether it accepts ids of already-succeeded deliveries), so baseline 3 applies.

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?

States a specific verb and resource ('Replay a ... webhook delivery') and narrows scope to 'dead-lettered or failed' deliveries, which distinguishes it from list_merchant_webhook_deliveries (inspection) and send_merchant_webhook_test (test send). It does not explicitly name those siblings, so the distinction is inferable rather than stated.

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?

'after fixing your endpoint' gives a concrete precondition for invocation, which is a real usage context rather than none. There are no explicit exclusions or named alternatives (e.g., use send_merchant_webhook_test first, or create a new delivery instead of replaying), so it stops short of full when/when-not guidance.

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