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

Annotations already declare this a safe idempotent read, so the bar is lower, yet the description adds real non-obvious context: a per-call price ($0.03 over x402 on Base), the prepaid x-credit-token header for unlimited calls, no free tier, and no API key requirement. These auth/cost details are exactly what annotations cannot express, though return shape and pagination are left to the output schema.

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 purpose and the b20_rebase contrast are front-loaded, and the pricing/auth sentences earn their place. However, the rhetorical triple 'no transfer, no per-account event, nothing in your tx history' and the em-dash-heavy cadence add length without adding information, diluting a fairly dense paragraph.

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 an output schema present, return values need not be explained, and the description still covers purpose, the sibling alternative, the downward-move flagging behavior, and the payment/auth model. It is complete enough to invoke correctly; only the exact output fields/history depth are left to the schema.

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 the sole parameter is documented in the schema as the B20 Asset token address. The description only restates 'Required input: address' without adding format, network, or validation meaning, so the baseline 3 is correct.

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 (replays the full MultiplierUpdated history) and resource (a B20 asset's multiplier rescaling), and explicitly distinguishes itself from the sibling b20_rebase ('shows today's value; this replays the full history and flags DOWNWARD moves'). An agent can select between the two without opening either 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?

Names the alternative (b20_rebase) and the condition that selects it (current value vs. full history of downward moves), plus a use context ('before you hold a rebasing RWA'). It stops short of explicit when-not-use or failure-condition guidance, so it falls just below the top band.

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