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

Annotations already declare write (readOnlyHint=false), openWorld, non-idempotent, non-destructive, so the safety profile is covered. The description usefully adds the 10-credit cost and the precise endpoint, but says nothing about duplicate-subscription behavior (relevant given idempotentHint=false), auth, or delivery mechanics.

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?

Lead sentence is front-loaded and the bracketed metadata is compact and scannable. The Group/Endpoint lines are arguably redundant with the tool name, but nothing is bloated and the whole thing is short.

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?

An output schema exists so return values need not be described, and annotations carry the safety profile. However, for a stateful webhook registration the description omits operational essentials such as how notifications are delivered, where to manage/unsubscribe, and duplicate handling, leaving it adequate but not fully complete.

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 67%; 'fields' and 'precision' are already well described in the schema, while 'url' has format/limit but no prose. The description reinforces that url is required and signals the cost, but adds no meaning (validation rules, target semantics) beyond what structured fields already convey.

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: 'Subscribe to natal-transit aspect threshold-crossings.' This distinguishes it from the many sibling webhook events (sign_ingress, retrograde_start, void_of_course_start, etc.) by the event category. It stops short of naming any sibling explicitly, so sibling disambiguation still depends on the agent parsing the event concept.

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?

Usage is only implied by 'Subscribe to...' – an agent can infer you call this when you want notifications for transit aspect threshold-crossings. No when-not conditions, prerequisites, or alternatives (e.g., the pollable stream_transit_alerts or generic webhooks_subscribe) are named. The cost and required-param brackets are metadata, not routing guidance.

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