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

With no annotations, the description carries the full behavioral burden. It does disclose a 5-result cap, which is genuinely useful, but adds nothing about auth, rate limits, or whether the 'free' quota is per-session or per-key. 'Soft-Offer outbound is OFF' is opaque internal jargon that conveys no behavior an agent can act on.

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?

It is short, but brevity here comes from omission rather than economy. The opening 'Free peek, max 5' and the trailing 'Soft-Offer outbound is OFF' are cryptic fragments that consume the front-loaded position without telling the agent anything actionable.

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 two parameters, no output schema, and no annotations, the description should explain the return shape and the meaning of the result cap. It instead leaves the size semantics, quota behavior, and output content entirely undocumented, so an agent cannot call this confidently beyond a bare postcode query.

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 only 50% and the postcode description ('Example EC1') is thin. The 'size' parameter is never mentioned in the description, and it is unclear whether 'max 5' overrides size or whether size means result count, page size, or record size. The description does not compensate for the coverage gap.

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 core resource is stated clearly: domestic Energy Performance Certificates for a postcode in England and Wales. However, the leading fragment 'Free peek, max 5' is unexplained jargon and no verb tells the agent what 'discover' actually does (list? search? sample?). Nothing distinguishes it from the sibling epc_pack beyond an implicit free-vs-paid hint.

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?

'Free peek, max 5' implies this is a trial/sample call rather than a full retrieval, and the England-and-Wales scope implicitly excludes other regions. But the description never says when to use this instead of epc_pack or how redeem_pack relates, leaving the routing decision to inference from the tool names.

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