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

Annotations cover the safety profile (write, openWorld, non-idempotent, non-destructive). The description adds real behavior beyond that: message rate is capped at one per update, every message carries an unsubscribe link, and no API key is required. That is substantive disclosure not present in the annotations.

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?

Dense and front-loaded, leading with the action and endpoint, then verification modes, then delivery constraints. Nearly every clause earns its place, though the parenthetical challenge explanation is slightly verbose.

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 3-parameter tool with no output schema, the description covers the essential unknowns: endpoint types, both verification methods, delivery frequency caps, unsubscribe behavior, and absence of auth. Little an agent needs to call 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 only 33% (only url documented), so the description must compensate. It does: it explains the semantics of the verify parameter (echo challenge vs well_known token file) and the kind distinction (webhook vs A2A endpoint), adding meaning beyond the bare enum values.

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+resource ('Opt in to Haven update notices') and the target endpoint types (webhook or A2A). An agent can tell this is a subscription action, distinct from get_updates, though it never explicitly names or contrasts with the unsubscribe_updates sibling.

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 explains the two verification flows (verify=echo vs verify=well_known) and the endpoint requirement, which is genuine operational guidance. However it never states when to choose this over get_updates or how it relates to unsubscribe_updates, so usage is only implied.

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