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

Annotations only set the safety profile (readOnly=false, destructive=false, idempotent=false); the description adds the operationally critical fact that the API key is shown once and cannot be re-read, plus exactly how to present it (Authorization: Bearer or X-API-Key). That is real behavioral context an agent cannot get from the schema or annotations.

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 action in a short first sentence, then uses the second sentence for return values. The parentheticals are dense but each clause (one-time key display, auth header syntax, ?ref usage) carries information the agent 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?

With no output schema, the description correctly covers what confirmation returns (API key, referral code) and how to use each. It omits failure behavior for an invalid/expired code and does not note that the call is non-idempotent, leaving minor gaps for a state-changing tool.

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 100% and includes a format example for the code (ABCD-2345) and the meaning of email, so the baseline is 3. The description only adds the provenance of the code (from partner_join), which is a thin addition over the schema.

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+resource (confirm the email address for the partner account) and explicitly ties the required code to its origin tool, partner_join. This distinguishes it cleanly from lookalike siblings such as partner_signin, partner_signin_code and partner_join without opening any schema.

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 the clear prerequisite that the code comes from partner_join, which establishes the workflow order (join -> confirm). It does not name or exclude alternative auth paths (partner_signin, partner_signin_code), so it stops short of full when/when-not guidance.

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