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

Beyond the annotations, it discloses the out-of-band confirmation flow (email link, user presses Confirm), the sign_in_url fallback if email fails, the instruction never to confirm on the user's behalf, and the privacy rule that the email is revealed only after mutual approval. It does not clarify the idempotency_key behavior, which the annotations declare as idempotentHint=false even though the schema offers an idempotency key.

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?

Front-loads the optionality and the owner_key rule, which are the decision-critical facts. It is denser than ideal with several colon-chained clauses, but nearly every sentence carries a distinct behavioral fact rather than filler.

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?

An output schema exists so return values need not be explained, and the description still covers the two non-obvious outcomes (same key back vs. new empty owner) plus the manual confirmation step. Nothing an agent needs to invoke this correctly is missing.

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%, so the baseline is 3, but the description adds real meaning for owner_key: sending an existing one preserves the person's listings and deals, while omitting it creates a new empty owner and orphans prior data. That consequence is not spelled out as starkly in the schema text.

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 ('sign in with the person's email') and immediately qualifies it as optional. It also contrasts with the sibling paths that make sign-in unnecessary (market_make_offer, market_create_listing), so an agent can place it in the workflow without opening other schemas.

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?

Explicitly says when NOT to call: 'You do not need sign-in to list or offer' and names the tools that mint an owner_key instead. It also gives the conditional branch for when to pass owner_key. Both the use case and the alternatives are stated.

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