preview_message_send

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

With no annotations, the description carries the full behavioral burden, and it does disclose an important trait: the tool is feature-gated and off by default unless the provider advertises an approved mutation capability. However, it does not state whether the preview has any side effects, what it returns (a diff or token), or that a separate confirmed-mutation call must follow.

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?

Two short sentences with zero filler, and the availability constraint is front-loaded after the purpose statement. Nothing is redundant.

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 simple two-parameter tool the description covers the availability gate but leaves the mutation lifecycle unexplained: what a preview produces and how it connects to execute_confirmed_mutation. With no annotations and no parameter documentation, an agent still has gaps before calling it correctly.

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 0%, and the description says nothing about the two parameters. The nested changes array (field/value/operation with set/remove) and the provider enum are only inferable from the raw schema, so the description does not compensate for the coverage gap.

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?

"Preview a message mutation" names a verb and resource, but "mutation" is vague: it does not tell an agent whether this previews a message send, edit, or delete, even though the tool name says message_send. It fits the sibling preview_* family pattern but lacks explicit differentiation from them.

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 gives a real gating condition (disabled by default, only usable when the provider advertises an approved mutation capability), which implies calling discover_provider_capabilities first, but it never names that sibling or explains the relationship to execute_confirmed_mutation. No explicit when-not guidance is given.

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