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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds real value beyond them by disclosing what comes back (headline rate, settlement timing, contract length, channels) and the provenance of regulatory identifiers from the FCA register and Companies House, including the caveat that they exist only 'where we found them'.

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?

Three sentences, front-loaded with purpose then filters then return content, with no filler. The trailing 'Read-only' duplicates the readOnlyHint annotation and is the one phrase that does not earn its place.

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 three-optional-parameter lookup with no output schema, the description covers purpose, filterable facets and return content well enough to call correctly. Minor gaps remain around result limits, pagination or ordering, which are not mentioned.

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 enum values are already documented, so the schema carries parameter meaning. The description only restates the three filter facets without adding syntax, matching behaviour, or combination rules beyond what the schema provides, 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 (Search) plus a precisely scoped resource (UK card-payment acquirers and processors in the MerchantHQ Card Acquirer Index). An agent immediately knows the domain, the dataset, and that results are acquirer records rather than, say, merchant accounts.

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?

The description tells the agent which facets can narrow a search (free-text query, tier, channel), which implies usage, but never states when this tool is the right choice or when it is not. With no sibling tools this omission is low-risk, but no explicit usage conditions or exclusions are given.

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