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

readOnlyHint=true already tells the agent this is a safe, non-mutating read, so the description's main added value is disclosing the HTTP endpoint (POST /api/v2/getaccperiods) and confirming the returned attributes. It reveals nothing about ordering, whether inactive periods are included, or whether authentication is required, so it is useful but not rich.

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?

Two compact clauses with no padding; the resource and returned fields are front-loaded. The trailing API endpoint is arguably internal plumbing an agent cannot use, but it is brief enough not to crowd out the signal.

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 parameters and no output schema, the description shoulders the burden of conveying what comes back, and it does so adequately by naming start, end and active flag. It would be complete at 5 if it mentioned result ordering or whether the list is exhaustive versus paginated.

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?

The tool takes zero parameters, so there are no parameter semantics to explain and the baseline of 4 applies. Nothing in the description misleads about inputs.

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?

Names the exact resource (accounting periods / financial years) and previews the returned fields (start, end, active flag), which cleanly distinguishes it from sibling list tools like merit_list_payment_types or merit_list_dimensions. It lacks an explicit verb in the description body, relying on the name and title ('List financial years') to supply it, so it stops just short of a 5.

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 when-to-use or when-not-to-use guidance whatsoever. It never says, for example, that this should be called first to resolve a financial-year identifier before invoking report tools like merit_balance_sheet, nor does it point to any alternative. The agent must infer the use case entirely.

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