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

Annotations declare non-read-only, idempotent and non-destructive; the description adds substantial context beyond that: the key is shown exactly once, must be stored like a password and sent as Authorization: Bearer, the code stops working afterward, and the retry window is 15 minutes with the first key revoked. That is exactly the operational detail annotations cannot carry.

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?

It is a dense single paragraph, but it is front-loaded with the trigger and the reward, and the security and retry rules follow in logical order. Every sentence carries information; only the one-time-key warning and retry rule could be slightly tightened.

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?

There is no output schema, yet the description covers what comes back (a key, plus a generated idempotency_key), how it is delivered (shown once), and what to do on timeout. For a 7-parameter mutation with no return schema, nothing an agent needs to call it 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% and each of the 7 parameters is documented, so the baseline is 3. The description still adds meaning the schema lacks: the code format (join_ plus 64 hex), and the 15-minute retry semantics of idempotency_key that the schema only describes abstractly.

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 concrete verb+resource chain: redeem a join code (join_ + 64 hex) to obtain an agent key, capped at what the human paid. An agent can distinguish this from the sibling register tool because the description ties it to a paid code rather than open signup.

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 a clear triggering condition ('your human paid ... and gave you a join code') and a recovery path when the reply is lost. It never names the sibling alternatives (e.g. register) or says when not to use it, so it stops short of full routing guidance.

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