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

Beyond the readOnlyHint/openWorldHint annotations, it discloses how fixed-date entries resolve to a next due date, the Europe/London default, the to_date filtering, and that period-dependent regimes (VAT, Corporation Tax, Companies House) return next_due null with a recurrence_rule. It also surfaces the x402 pricing/API-key auth model, which is real operational context. Return shape is only partially described, keeping it short of a 5.

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 core listing behavior is front-loaded and the two sentences carry dense, non-redundant information. The second sentence is long and packs pricing alongside result semantics, which slightly blurs the structure.

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 must explain the returned fields, and it does so concretely (next_due, recurrence_rule, the null case). Combined with annotations covering the read-only profile and 100% schema coverage on both parameters, an agent has everything needed to call it 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 already 100%, so the schema baseline applies, but the description adds genuine meaning: from_date is not just a boundary but the anchor used to compute the next due date, and to_date truncates the result set. That is semantics the schema's terse 'YYYY-MM-DD' pattern does not convey.

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 ('List UK tax/payroll deadlines') and elaborates on what the listing contains, which clearly separates it from rate/company/rule siblings. It never names an alternative tool, so differentiation is by domain rather than explicit contrast.

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 implied through the date-range mechanics: the caller infers this is for enumerating deadlines inside a window. There is no explicit statement of when to prefer this over check_uk_business or search_rules, and no exclusions or prerequisites are given.

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