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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety and idempotency profile is fully covered structurally. The description adds essentially nothing beyond that — no auth requirements, no note on whether the data is historical or live, no freshness or rate-limit context. Given the lowered bar with full annotation coverage, a 3 is right.

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?

Two very short fragments, front-loaded with what is returned before the example query. Nothing is padded. The first fragment is slightly elliptical (no verb), which costs it a point but does not hurt comprehension.

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?

This is a simple single-address read tool, and an output schema exists so return values need no explanation. The description covers the subject and the payload fields, which is enough for correct invocation. It stops short of noting whether a non-referrer address returns empty data, a minor but real gap.

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?

There is a single required parameter with 100% schema description coverage, including the 0x address pattern, so the schema carries the full burden. The description only implies that the address is the lookup subject ("An address's referral code") and adds no meaning such as whether EOAs and contracts behave differently. Baseline 3 applies.

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 specific resource (an address's referral data) and enumerates the returned fields: referral code, tier, referred volume, earnings. It is a noun phrase rather than a verb+resource statement, but the intent is unambiguous. It does not distinguish itself from adjacent siblings such as get_tiers or get_points, which is the only thing keeping it from 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?

The quoted example question ("How much have my referrals earned?") implies when to reach for this tool, which is useful intent-matching. However, there is no explicit when-not guidance, no mention of how it differs from sibling lookups like get_tiers or get_account, and no stated prerequisites. Usage is implied rather than directed.

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