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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is known. The description contributes genuine behavioral context beyond that — an event with no list falls back to the default channel — but it never states whether a call replaces or merges the entire existing routing config, which is the key destructive consequence an agent needs.

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?

Purpose is front-loaded in the first sentence, followed by the event vocabulary and then the two nested-field semantics. The long event list earns its place because the values are not in the schema; the only slight redundancy is restating routing.default_channel_id and routing.events in two consecutive sentences.

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 single nested-object parameter with no output schema and rich annotations, the description covers structure, fallback behavior, and valid event names. It is still missing the replace-vs-merge semantics implied by destructiveHint=true and any note on format/permissions for the channel ids, which leaves an agent under-informed before a destructive write.

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%, but the schema only says "default_channel_id and events." The description carries real weight by explaining that routing.default_channel_id is the fallback and routing.events maps an event name to a list of channel ids. It also enumerates the ten valid event names, which is critical since the schema has no enums and would otherwise leave the agent guessing at accepted 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?

"Chooses which verified channels receive each event" gives a specific verb (chooses) and resource (event→channel routing), which is clearer than the sibling names alone. It does not explicitly contrast with nearby tools like set_number_routing, set_notification_preferences, or list_routing_options, so the boundary is inferred rather than stated.

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 mechanics of routing but never says when to reach for this tool versus set_number_routing, set_notification_preferences, or add_callback_channel. The only prerequisite hint is the word "verified" in the first sentence; there is no when-not or alternatives guidance.

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