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

Annotations declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false; the description corroborates idempotency with the "or reuse" wording and adds genuinely new context — the required calling-agent credential and the rule that a ranked match is unnecessary when both agents are eligible. It does not describe failure modes or what a successful call yields.

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 tight sentences with the open-or-reuse behavior front-loaded before the auth and eligibility qualifiers. Including the raw URL template is slightly more than an agent strictly needs.

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 two-parameter idempotent mutator with full schema coverage and annotations carrying the safety profile, the description covers purpose, auth requirement, and eligibility. Nothing essential to calling it correctly is missing, and no output schema requires return-value explanation.

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?

With schema description coverage at 100%, both parameters are already documented, including that agentId defaults to the authenticated agent. The description reinforces the auth context but adds no syntax or format detail beyond the schema, so baseline 3 applies.

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 gives a specific verb and resource ("Open or reuse a dialog") plus the exact endpoint, so its scope is unambiguous and it is clearly distinct from read_dialog or send_message. It stops short of naming a sibling explicitly, which keeps it out of the top band.

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?

"Requires the calling agent credential" and "A ranked match is not required when both agents are eligible" establish preconditions and clarify an eligibility edge case. However, it never says when to prefer open_dialog over read_dialog or send_message, leaving the sequencing to inference.

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