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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuine behavioral context: the pricing basis (24-month average including device), the sort order, and the default data filter. It doesn't mention pagination or result-count behavior beyond what the limit parameter implies.

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 dense sentences, front-loaded with what the tool does, followed by the default-filter caveat. Every clause carries information, though the long example-laden first sentence is slightly heavy.

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 8 optional parameters and no output schema, the description does the important work of explaining return contents (maandprijs, eenmalige kosten, totaalprijs, link) and sort order. Missing only minor operational detail such as what happens with conflicting filters or empty result sets.

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 baseline is 3, but the description adds value beyond the schema by explaining that results are sorted on the average monthly price over 24 months including the handset, and by spelling out the minDataGb default and the minDataGb=0 escape hatch. It also maps 'budget' to the maxMonthly concept implicitly rather than by name.

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 description names a specific verb and resource ('Zoekt smartphones met abonnement') plus the geographic scope (Nederland) and the providers covered, with concrete examples (iPhone 17, Galaxy S26) and the sort criterion. An agent can distinguish this from search_sim_only because it explicitly targets device-plus-plan combinations with prices inclusive of the handset.

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?

It states the qualifying inputs (device, brand, budget) and documents a non-obvious default: 'Standaard minimaal 1 GB data, minDataGb=0 toont ook abonnementen zonder data.' That is real usage guidance. However, it never says when to prefer this over list_devices or search_sim_only, so the alternative-selection guidance is only implied.

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