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

The annotations declare readOnlyHint=true, yet the description says 'Register ... to earn commission ... forever,' which strongly implies persistent state changes. This is an annotation contradiction. The description also does not disclose behavior on duplicate registration or a missing referralCode, though idempotentHint partially covers that.

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?

The description is two short sentences, is front-loaded with the main purpose, and adds only the relevant cost note. No words are wasted.

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?

Given the simple optional parameter, rich annotations, and output schema, the description could be sufficient. However, the readOnlyHint contradiction makes the overall context unreliable and could cause an agent to select or invoke the tool incorrectly.

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 schema already describes the single optional referralCode parameter thoroughly, including the required format (PLAZA-REF-XXXXXXXX). The prose adds no additional meaning beyond the word 'referral code,' so the baseline of 3 applies given 100% schema description coverage.

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 names a concrete action ('Register with a referral code') and a clear outcome ('earn commission on referrals forever'). It goes beyond the title, but it does not differentiate plaza.register from siblings such as plaza.referral_kit or plaza.earnings, so it stops short of a 5.

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?

'Free to call' gives a useful cost signal and the purpose clause implies when to use it, but the description never states when not to use it or names an alternative, such as plaza.referral_kit. The usage guidance is therefore only implied, not explicit.

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