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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety bar is low. The description adds genuinely useful context: the credential switches to the user's allowance, trial and plan, and an interactive sign-in prompt may occur. However, 'links this connection' implies a state change on the connection, which sits in mild tension with readOnlyHint=true and is not reconciled.

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?

Effect is front-loaded and the triggers follow in one sentence, so it reads well. The closing sentence ('If they aren't signed in, Claude will ask them to sign in') is circular and partly redundant with the trigger already stated.

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 zero-parameter, no-output-schema tool with rich annotations, the description supplies the missing decision context: when to invoke it and what quota behavior changes. It does not cover what the agent should do after the call (e.g., retry contact_check), which would close the loop.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline applies. The description correctly conveys that the call is parameterless and driven by the user's sign-in state instead.

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?

States a specific verb and resource ('Links this connection to the person's own Precleared key') and immediately explains the effect on quota/trial/plan, so the agent knows exactly what the call accomplishes. It is clearly distinguishable from contact_check and verify_receipt.

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?

Gives two concrete triggers: the user asking to sign in/connect, and contact_check reporting that free checks have run out. No explicit 'do not use when' condition or alternative is offered, but the routing to contact_check covers the main decision point.

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