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

Annotations only say readOnly=false, idempotent=false, openWorld=true; the description goes well beyond that with the double opt-in confirmation-then-digest flow, https-only/public-host restriction on webhooks, HMAC-SHA256 signing, and the fact that a webhook signup returns the signing secret once, a private feed token, and the signed verification ping result. That is precisely the behavioral context an agent needs before committing a side effect.

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 benefit and the two modes are front-loaded, and each sentence carries distinct information (opt-in flow, webhook constraints, return payload, safety constraint). It is on the dense/long side, but there is little padding to cut.

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?

With no output schema, the description still describes the return payload (one-time signing secret, feed token, verification ping result), covers both signup paths, and matches the non-idempotent annotation by implying each signup yields new credentials. Nothing an agent needs in order to invoke it correctly is missing.

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: what email triggers (confirmation link, then digest only on days with news), what webhook_url requires (https, public hosts, signed POSTs), and what a webhook signup returns. Topics are left to the schema, which is acceptable since it documents them fully.

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 ('subscribe') plus the resource and benefit: newly verified offers ~24h before they go public, plus closures and changes. This cleanly separates it from siblings like early_offers (which surfaces offers) and recently_changed, so an agent can route 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 explicit routing between the two modes ('email (a person)' vs 'webhook_url (an agent)') and a strong use constraint ('Only subscribe an address or URL the user asked you to'). What's missing is an explicit statement of when to prefer a sibling tool (e.g. reading early_offers instead of subscribing), but the mode selection is unambiguous.

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