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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely new behavioral context: it is free, it is a fixed sample, no other token input is accepted, and it does not make a payment — all useful for an agent deciding whether invoking it has any cost or side effects.

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 short sentences, no wasted words, with the core identity (free fixed USDC sample) front-loaded. The qualifiers that follow both do real work.

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 parameters and no output schema, the description covers what the tool is and its constraints adequately. The only gap is that it does not hint at what 'on-chain facts' are returned, which matters slightly more when no output schema exists.

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 are zero parameters, so the baseline is 4. The 'No other token input accepted' clause usefully explains why the schema is empty and preempts an agent from trying to pass a token address.

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?

Names a specific resource (native USDC on-chain facts on Base) and a specific mode (free fixed sample/preview), which is more precise than a generic 'get facts'. It also implicitly distinguishes itself from the sibling base_token_facts by stating only USDC is accepted, though it never names that sibling.

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 description implies usage (a free, fixed preview rather than a parameterized query) and rules out payment, but never states explicitly when to choose this over base_token_facts or base_token_allowance. The routing guidance is inferable rather than stated.

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