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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds meaningful context beyond them: the data comes live from HMRC MTD (open-world external dependency) and requires an HMRC MTD connection. Missing are any call-out on HMRC API throttling or behaviour on a disconnected account.

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?

Front-loads the resource and its payload, then triggers, then the precondition. The long parenthetical is dense but every element is useful; only minor tightening is possible.

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 tool with no output schema, the description compensates by listing the returned fields and stating the connection requirement. Pagination and behaviour for a not-connected account are the only notable gaps.

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 schema already documents `from`/`to` defaults and the ~1-year range cap plus the `company` scoping rule. The description adds no parameter-level detail beyond the schema, so the baseline of 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 (read) and resource (VAT obligations from HMRC MTD) and enumerates the returned fields — period keys, start/end dates, due dates, Open/Fulfilled status — which cleanly separates it from get_hmrc_vat_liabilities (amounts owed) and get_hmrc_vat_payments.

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?

Gives three concrete user-question triggers plus a reconciliation use case, which is clear situational guidance. It stops short of explicitly naming alternatives to avoid (e.g. get_vat_periods for local periods) or exclusions, so it is not a full 5.

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