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

Annotations only cover readOnly/openWorld; the description adds substantive behavior an agent needs: it is public ARES data, returned codes are raw and un-normalized, and each successful call costs $0.002 in USDC via x402 on Base/Solana/Arc with failed calls not charged. The pricing/payment-rail and no-charge-on-failure disclosure is exactly the kind of context annotations cannot convey.

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 the resource and identifier, then the returned fields, then the one caveat (raw codes) and cost. No filler; every clause carries information an agent would otherwise have to guess.

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 one-parameter lookup with an output schema present, the description covers the remaining unknowns: data source, code normalization, and the billing model including failure behavior. Nothing an agent needs before calling is missing.

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 description coverage is 100% and the single `ico` parameter is already documented with format and an example (45274649). The description's restatement that IČO is an 8-digit company number adds no meaning beyond the schema, so the baseline 3 applies.

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+resource: fetching a Czech ARES business register record by IČO, and enumerates exactly what comes back (name, DIČ, legal form code, address, dates, tax office). The country/registry scoping cleanly separates it from siblings like b2b_slovakia_rpo_companies, gov_krs_poland or b2b_brreg_norway_companies without needing the 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 description makes the triggering condition clear: you must have an 8-digit IČO for a Czech entity. It gives clear context but names no alternatives or exclusions (e.g., what to use for a company name search or for non-Czech entities), so it stops short of explicit when/when-not routing.

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