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

With no annotations, the description carries the burden well: it discloses the firing semantics (at most once per period_days while spend stays over threshold), the webhook POST delivery, and the return value. It omits auth/permission requirements and webhook failure/retry behavior, which an agent configuring an endpoint would benefit from knowing.

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?

Three dense sentences that front-load the core action and trigger, then scoping, then firing cadence, then return value. No filler or restatement of the name.

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?

No output schema, but the description supplies the return value (alert ID) and the key operational semantics. Combined with 100% schema coverage, an agent has enough to invoke it correctly; only auth/prerequisite context and webhook failure handling are 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 description coverage is 100%, so the baseline is 3. The description reinforces the semantics of org_id (omit for total) and the threshold/period interaction, but adds little that the schema's own parameter descriptions do not already state.

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 ("Register a webhook URL to receive notifications") plus the exact trigger condition — recorded spend from record_usage crossing a USD threshold in a rolling window. This is clearly distinguishable from register_price_alert, list_budget_alerts, and delete_budget_alert by naming the data source and alert type.

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 clear selection context: use org_id to scope to one organisation, omit it to monitor total spend, and the alert fires at most once per period_days. It doesn't explicitly name sibling alternatives (register_price_alert for price drift, list_budget_alerts for review), so the routing guidance stops short of full when-not coverage.

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