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

Annotations already declare destructiveHint=true and idempotentHint=false, but the description goes further by enumerating exactly what moves (messages, files, pending email), how tags are handled, and that the source conversation closes. 'This cannot be undone' quantifies the irreversibility beyond the bare hint, which is exactly what an agent needs before calling a destructive tool.

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?

A single dense sentence that front-loads the operation, then the side effects, and ends on the irreversibility warning. No filler and nothing buried.

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 destructive two-parameter mutation with no output schema, it covers preconditions, side effects and reversibility. It does not say what the call returns or confirm success behavior, a minor gap given the absence of an output schema.

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% and both parameters are fully documented there, including the list_merge_candidates hint, so the baseline is 3. The description adds only the same-contact constraint on the pair, which is useful but marginal against what the schema already supplies.

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?

Names a specific verb (merge) and resource (conversation) and pins the direction of the operation — 'a conversation into another' — so the agent can tell conversationId and targetId apart. It also states the scope constraint (same contact), which no sibling tool shares.

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?

'from the same contact' establishes the precondition that makes a merge valid, which is real usage context. It stops short of naming alternatives (e.g. merge_duplicate_contacts, or the list_merge_candidates sibling referenced only in the schema), so the routing guidance is contextual rather than explicit.

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