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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world); the description adds genuinely new behavior: it only reads stored data and fills gaps with "unbekannt", and it returns a deep link to objelio.de where the user can save listings and contact agents. The only omission is what happens with invalid or deleted listing ids, and the return shape is covered by the 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?

Two sentences, front-loaded with the comparison scope, followed by data-limitation and return-value notes. Every clause carries information an agent would not otherwise have.

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 low-complexity, single-parameter read tool with full schema coverage, an output schema, and complete annotations, nothing material is missing: purpose, compared attributes, data-freshness caveat, and the returned link are all stated.

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 single parameter already documents its 2–3 item constraint, so the description only restates "two or three listings" plus the provenance from search_listings. Baseline 3 applies since the schema does the heavy lifting on semantics.

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?

Names a specific verb (compares) and resource (two or three listings) and enumerates exactly which attributes are compared, so the agent knows the output surface without opening the schema. It also ties itself to the sibling that produces the inputs (search_listings), differentiating it from get_listing (single) and search_listings (discovery).

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 states the input provenance ("two or three listings from search_listings"), which implies the correct call sequence: search first, then compare. It does not explicitly say when not to use it, e.g. that a single listing should go through get_listing, so the routing guidance is clear but not exhaustive.

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