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

Adds substantial context beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false): the 12-month duration, the one-credit consumption, the exact failure conditions (photo/description thresholds), and the required Cotlet API key scope. This is the description doing real behavioral work that structured fields do not cover.

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-loaded with the core action and then layered constraints, so an agent gets the essentials first. Slightly redundant, repeating the photo/description requirement ('Needs 3 photos and a 200 character description' then again as failure conditions), which keeps it from a 5.

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 mutation with no output schema, it covers duration, credit cost, eligibility constraints, credit source, confirmation behavior, network reach, and auth requirements. Nothing an agent needs to invoke it correctly is missing.

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%, so the baseline is 3, but the description adds meaning: highlight_ids must be chosen from the 'Premium Listings highlights chart' and up to 2 are allowed, and it clarifies that listing_id must refer to an eligible listing (photo/description thresholds).

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 ('Upgrade'), resource ('one listing'), and target state ('Premium') with concrete attributes (12 months, 2 highlights). It is clearly distinguishable from sibling zoopla_feature_listing and other listing tools.

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 explicit prerequisites (3 photos, 200-char description) and confirmation policy ('confirm each call; you can switch that off'), plus a standing instruction to confirm with the user before each call. It does not explicitly name when to choose this over sibling upgrade/feature tools, so it stops short of a 5.

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