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

Annotations declare readOnly/idempotent/openWorld, but the description adds real substance beyond them: it discloses the register source, the 'up to three matches, registered first' cap on name search, that trustees are counted but never named, and the England-and-Wales-only scope. It does not discuss rate limits or response shape, but for a read lookup this is solid extra context.

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 question-led framing is front-loaded and effective, but the middle is a dense comma-spliced list of attributes that is harder to scan than it needs to be. The trailing licensing sentence is legally necessary but adds bulk.

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 single-parameter read tool with no output schema, the description enumerates what the agent can expect back (status, dates, flags, six years of accounts, governance) and sets jurisdiction limits. It does not explain the response format, but as a lookup it tells the agent enough to call and interpret it correctly.

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% and the schema already documents the single parameter's three accepted forms, so baseline is 3. The description goes further by explaining that company-number matching is done via the Companies House number held on the register, and that group members use a hyphenated charity number — meaning beyond the raw schema.

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 triple question (registered? in good standing? what do accounts say?) against a named authoritative source, the Charity Commission for England and Wales. It clearly distinguishes itself from compliance-lookup siblings like cqc_check and sra_check by naming the exact register and jurisdiction.

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?

It tells you three lookup modes (charity number, company number via Companies House, name with up to three matches), which implies when each is usable. But it never states when to prefer this tool over siblings such as accounts, registers, or distress_signals, nor any exclusion criteria.

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