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

Annotations already declare readOnly/openWorld/non-destructive, and the description goes well beyond them: the 404-on-unknown-hash behavior, the billing model ($0.01 per call via x402 USDC or card key, first 25 free, failed calls free), and the explicit warning that calls are not idempotent in practice because each repeat is charged. That last point directly reinforces idempotentHint=false with actionable context.

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?

Front-loaded with purpose, then alternatives, then input contract, then pricing — a sensible order with no filler sentences. It loses a point for mild redundancy: the 0x-prefixed 64-hex format restates the schema, and 'reads or computes only and changes nothing' restates readOnlyHint.

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 return-value disclosure and does it by listing the fields returned (including the 4-byte selector and block). Cost, error behavior, and sibling routing are all covered, leaving nothing an agent needs to call this correctly.

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%, so the baseline is 3; the description adds the 404 consequence for an unrecognized hash and supplies a concrete example value, which is real value beyond the schema. It does duplicate the format string already in the schema, keeping it from a 5.

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 and resource ('Look up an Unichain transaction by hash') and enumerates the returned fields (sender, recipient, value, nonce, gas limit, selector, block). It explicitly names the siblings it is not — unichain_receipt for status/fees and unichain_logs for events — so an agent can route correctly without opening schemas.

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?

Gives explicit when-to-use ('see what was sent or whether it exists') and when-to-use-something-else, naming both alternatives and the exact conditions that select them (success/failure and fees -> unichain_receipt; emitted events -> unichain_logs). It also covers the negative case: an unknown hash returns 404, uncharged.

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