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

Annotations already indicate a mutating, non-idempotent operation, and the description's 'outbound' phrasing aligns with readOnlyHint=false. The description adds the prerequisite of a valid contact channel and clarifies which body fields are mandatory per channel. It doesn't contradict annotations and provides useful constraints beyond them.

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 short sentences front-load the core action, then cover channel-specific requirements and the contact precondition. Every sentence earns its place; no filler or duplication.

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 6-parameter tool with conditional fields and no output schema, the description covers the essential invocation logic and preconditions. It is slightly incomplete in not describing the response shape or what happens if the contact's channel is invalid, but annotations and schema fill the remaining gaps.

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?

While schema coverage is 100%, the description adds the cross-field rule that Email requires subject plus either html or message, and SMS requires message. This conditional requirement isn't fully expressed in the schema's required array, so the description materially helps the agent assemble valid parameters.

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?

The description opens with a specific action, 'Send an outbound message to a contact via SMS or Email,' identifying the verb, resource, and channels. This clearly distinguishes it from sibling read tools like ghl_get_messages and from resource-specific senders like ghl_send_invoice or ghl_send_estimate.

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?

It gives concrete invocation guidance by channel: Email requires subject and html (or message), SMS requires message. It also states a precondition, 'The contact must have a valid phone/email for the chosen channel.' It doesn't explicitly name alternatives, but the context is clear enough for an agent to know when to call it.

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