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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds value beyond them: bounded source-order output, reported truncation, returned provenance/metadata, and an explicit failure-handling rule against inferring content. Return-format detail is partially redundant with the existing output schema.

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 trigger condition is front-loaded in the first sentence and the total length is short. The source-attribution line is slightly redundant with the title, but it earns its place as an allowlist/trust signal for an open-world fetch.

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 a full output schema and complete annotations, the description supplies the remaining essentials: read-only fetch semantics, truncation behavior, provenance return, and the do-not-infer-on-failure rule. The only gap is not telling the agent where to obtain a reference or family slug when it has none.

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%, so all four parameters (including the manual_url OR family+reference alternative and the 500–20000 max_chars bound) are already documented in the schema. The description mentions 'bounded' text and truncation reporting but adds no syntax or selection guidance 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?

The description states a specific verb (read) and a specific resource (a cited HMRC internal-manual page), and the 'cited ... must be read' framing implicitly separates it from the search tools in the sibling list. It does not, however, name a sibling such as hmrc_search_guidance or legislation_get_section to make the boundary explicit.

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?

'USE THIS TOOL WHEN a cited HMRC internal-manual page must be read' gives a clear triggering condition, and 'if retrieval fails, do not infer the page's contents' supplies a useful negative rule. Missing is the prerequisite path: when the agent only has a topic, it should search for a reference first, and no alternative is named.

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