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

With no annotations, the description carries the full burden. It discloses the return types (table, single threshold, verdict with headroom math) and the business rule (turnover above cap forces upgrade). It does not explicitly state 'read-only' or mention auth/rate limits, but the use case strongly implies a read operation; still, a small gap remains.

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?

The description is dense but well-organized: purpose, thresholds, business rule, call modes, and exclusions. Every sentence serves a purpose; the threshold list is necessary. Minor redundancy with the schema's parameter notes prevents a 5.

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 conceptually covers all three return forms and all parameter combinations. It also warns about excluded inputs. It does not detail the exact JSON response structure or error handling, but for a simple lookup this is acceptable.

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 have thorough descriptions (currency, conditional usage, excluded inputs). The tool description repeats these semantics and adds only the threshold values and 'headroom math' output concept, which does not significantly raise the value beyond the 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?

The description states a specific verb ('Return'), resource ('HelloBooks Free-plan annual-invoice-turnover thresholds'), and scopes it to 8 priced markets with actual values. It clearly distinguishes itself from the analysis/compliance siblings by focusing on eligibility thresholds and verdicts.

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?

It explicitly enumerates the three calling modes: no args for the full table, with country for a single threshold, and with country plus annualInvoiceRevenue for a freeEligible verdict. It also lists what inputs are NOT used (bank-feed total, cash receipts, gross transaction volume), preventing misuse.

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