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

The readOnlyHint annotation already covers the safety profile, and the description adds the non-obvious caveat that any ERC-20 address is also valid when paired with amountBaseUnits, meaning the listed symbols are not an exhaustive set. It says nothing about rate limits or response format, but for a zero-parameter read-only lookup that is a modest gap.

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?

A single sentence, front-loaded with the list contents and ending with the actionable caveat about ERC-20 addresses. Every clause carries information; nothing is redundant with the title or annotations.

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?

For a zero-arg read-only tool with no output schema, the description enumerates the fields the agent will receive (chains, chain ids, native tokens, token symbols), which is exactly the needed compensation. It stops short of describing the container format or any ordering, a minor omission given the simplicity.

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 tool takes zero parameters, so there is no parameter semantics to explain and the baseline of 4 applies. The description does not waste space restating an empty schema.

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 (list) and enumerates the exact resources returned: supported chains, chain ids, native tokens, and accepted token symbols. It also names the sibling tool swap_quote as the consumer of this data, so an agent can distinguish the lookup tool from the quoting tool 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?

The tie to swap_quote ('token symbols accepted by swap_quote') makes the when-to-use context clear: consult this before quoting. It does not spell out an explicit exclusion or say 'call this first', so it falls just 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.