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), and the description adds real context on top: every result carries source URL, checked date and quote, and unknown values stay null and never satisfy positive filters. That null-handling rule is a non-obvious semantic that directly affects filter interpretation and is not derivable from annotations or 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?

Four sentences, purpose front-loaded, no filler. The long filter enumeration is dense but each item maps to a parameter, so it earns its place; a short list format would read more cleanly.

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 13-parameter read-only query tool with no output schema, the description covers filtering, sorting, result provenance and null behavior, which is what an agent needs. Minor gaps remain around pagination/limit behavior and whether commitment_months is a maximum or exact match.

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 46%, so the description must compensate, and it largely does: it names nearly every parameter and adds meaning beyond the schema, e.g. data_gb as a minimum threshold, the unlimited-calls boolean semantics, and the fact that minutes/SMS/no_commitment/roaming_eu_gb still work. Only limit and commitment_months semantics (minimum vs exact) are left unstated.

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 and resource (compare sourced CZ and SK mobile tariff records) and even names the backing dataset file, which pins down the exact scope. An agent can distinguish it from siblings like compare_internet, compare_digital and compare_energy purely from the domain and market named.

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?

Explicitly declares country as required and explains why (results and currency stay within one market), then enumerates the usable filter sets and the two sort orders. It also carves out the legacy-style filters so the agent knows both filtering styles are valid, leaving no ambiguity about how to call it.

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