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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; the description adds genuinely useful behavior beyond that — the pricing method (each token valued as the fiat currency it tracks, benchmarked to an independent daily reference), the presence of a margin of error, and that the result is signed. It stops short of saying what happens for an unrecognized tx, an unsupported token, or a failed lookup.

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?

One front-loaded sentence that leads with the outcome ('what a swap really cost') before the mechanics. The long parenthetical enumerating ten stablecoin tickers is the weakest part — it is informative but bloats an otherwise tight definition, and 'and others' undercuts the enumeration anyway.

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 output schema, the description carries the return-value burden, and it only gestures at the shape ('token out and token in, each priced ... and signed') without naming fields or units. For a two-parameter read-only lookup this is workable, but an agent cannot predict the response structure or how the margin of error is expressed.

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 both parameters already document the tx hash format and the chain values, so the schema carries the load. The description restates the chain list and clarifies that the hash must be the swap's own transaction, but adds no format, normalization, or chain-specific caveats beyond that.

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 states a specific computation (the true cost of a stablecoin FX swap) and the exact input that identifies it (a DEX transaction hash), so the agent knows this is a per-transaction cost decomposition, not a route quote or a payment record lookup. It is distinguishable from quote/corridor siblings, but it never names a sibling (e.g. swapeazi_landed_cost) to sharpen that boundary.

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?

Usage is only implied: 'from its transaction hash' signals this runs after a swap has already settled, and 'Free' hints it can be called liberally. There is no explicit when-to-use statement, no when-not-to-use, and no pointer to the alternative to use for pre-trade pricing or for non-DEX payments.

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