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

Annotations already declare readOnlyHint, non-destructive, and closed-world, so the safety profile is covered. The description adds useful domain context ('Updates are cumulative from 6 April') and implies a next-deadline indicator, but says nothing about return shape, ordering, or behavior for years outside the enum.

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?

One sentence plus one short supporting clause, front-loaded with the core action and resource. No filler; the cumulative-updates note earns its place by explaining the deadline 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?

For a read-only, single-optional-parameter lookup with full annotation coverage, the description gives enough to call it correctly. Without an output schema it could say a bit more about what the returned list looks like, but nothing critical 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 taxYear parameter carries its enum and default ('Defaults to the current tax year') in the schema. The description's 'Updates are cumulative from 6 April' adds interpretive context for the returned periods but no parameter-level detail beyond the schema, so 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 (list) and resource (Making Tax Digital quarterly update periods and deadlines), plus a distinctive extra output ('which one is next'). The scope is clear enough to separate it from check_mtd_status and prepare_quarterly_update, though no sibling is named explicitly.

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 only implied: an agent can infer this is for looking up statutory MTD deadlines, but there is no explicit when-to-use, when-not-to-use, or pointer to an alternative such as prepare_quarterly_update for acting on a deadline.

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