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

The annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds genuine context beyond them: a 2-credit cost and the fact that date-based queries are gated behind paid plans. It does not say what actually happens on a free plan when year/month/day are supplied (error, silent drop, or partial results), which is the most important remaining behavioral unknown.

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 opening "Historical Events: Historical Events is..." restates the title twice before reaching the substance, which wastes the most valuable front-loaded position. Once past that, the two-sentence body is dense and carries real information (keyword search, descriptions, plan-gated dates, cost).

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?

An output schema exists, so return values need no explanation, and all four parameters are documented in the schema. What is missing is behavior around the all-optional parameter set: what a call with no arguments returns, whether keyword and date filters compose, and result limits or pagination. For an open-world lookup with zero required params, those gaps are material but not severe.

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 per-parameter meaning is already documented and the baseline would be 3. The description earns the bump by disclosing that the year/month/day parameters are only usable on paid plans, which is essential semantics for three of the four parameters that the schema does not convey. It does not clarify whether text combines with date fields via AND logic, nor what a no-argument call returns.

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 and resource: it searches historical records by keyword and returns matching events with detailed descriptions. That clearly separates it from lookalike siblings such as WorldHolidays, LiturgicalCalendar or NobelPrizes. It stops short of naming an explicit alternative, but the purpose itself is unambiguous.

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?

There is no explicit when-to-use or when-not-to-use guidance relative to the many other date/history-adjacent siblings. The one real usage cue is the plan-gating note: exact calendar dates and year/date queries require a paid plan, which implies keyword search is the free path. That is implied usage rather than stated routing.

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