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

Goes well beyond the annotations (non-idempotent, open-world, non-destructive) by disclosing the verification mechanics: email/SMS/WhatsApp require a code, webhooks must pass a signed test ping, SMS is subject to country rules, and — critically — the webhook secret is returned only once. That last point is a one-time-display hazard the agent could not learn from any structured field.

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?

Five short sentences, each carrying distinct information, with the core action and accepted types front-loaded and the one-time-secret warning placed last for emphasis. No filler.

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 non-idempotent mutation with no output schema, it covers the verification flow and the one-time secret, which is what an agent most needs. It omits what happens on duplicate adds, how 'default' interacts with existing channels, and never names verify_callback_channel, leaving the follow-up step implicit.

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 75%, so the baseline is 3, but the description adds real semantics by pairing each enum type with what the destination must be (email address, webhook URL, phone number, chat thread) and flagging the verification each type triggers. It says nothing about 'label' or when to set 'default', so it falls short of full coverage.

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?

Specific verb plus resource ('Adds an ... callback channel') with the full enumeration of channel types the tool accepts. It is clearly distinguishable from list_callback_channels, remove_callback_channel, and verify_callback_channel in the sibling set.

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 implied rather than stated: an agent can infer this registers a new channel, and the mention of codes and a signed test ping hints at a verification step. However, it never explicitly tells the agent to follow up with verify_callback_channel, nor does it state when to prefer this over that sibling or what happens if a channel already exists.

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