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

Annotations already declare idempotent=true, destructive=false, so the safety bar is lower, but the description adds substantial context: null clears, a new URL requires the key's webhook secret (409 webhook_secret_missing), invalid hosts yield 400 bad_webhook_url, the key's event filter applies, redelivery uses the recorded URL, and the call is free. The only gap is what the successful response looks like.

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 lead sentence is well front-loaded, but the remainder is a dense run-on mixing endpoint paths, parenthetical asides, and status codes, with noticeable redundancy (the PUT /api/v1/webhooks/url path appears twice, and the closing 'The same as PUT /api/v1/webhooks/url' repeats the opening). It could be restructured into shorter, single-purpose statements without losing content.

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 2-parameter mutation with annotations but no output schema, the description covers prerequisites, validation, precedence, side effects, and cost — nearly everything needed to invoke it correctly. The one omission is the shape of the response after a successful set, which the description sidesteps by pointing at get_job_webhook.

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%, so the baseline is 3, but the description adds real semantics beyond it: the precedence rule for which URL a job actually uses, the fact that clearing never requires the secret, and the https/public-host validation rule mirroring a job's webhook_url. The null-to-clear behavior is largely restated from the schema rather than extended.

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?

Opens with a specific verb+resource and scope: 'Set a default webhook URL for your key's job events', including the exact event types covered. It then actively distinguishes itself from siblings by name (get_job_webhook, set_webhook_events, set_usage_alert), so an agent can route correctly without opening another 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?

Gives an explicit when-to-use rationale ('so you don't have to send webhook_url with every job'), names the read counterpart (get_job_webhook), the related filter tool, and an explicit exclusion ('doesn't change usage alerts'). It even states the resolution precedence, which tells the agent exactly when this tool's value takes effect versus a per-job override.

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