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

With no annotations, the description carries more burden, but it does disclose the key behavioral trait that missing inputs fall back to documented defaults. It also enumerates the outputs, which is useful given there is no output schema. However, it does not describe whether the calculation is pure/read-only, what the output format looks like, or any constraints beyond what the schema already states.

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?

The description is short and front-loads the action plus output list, but the opening repeats 'EU drivers' hours calculator: driving time and rest periods calculator' redundantly. The final sentence about defaults is useful, but the overall phrasing could be tighter.

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?

Given five optional parameters with full schema descriptions and no output schema, the description is nearly complete: it names the outputs and notes default fallback behavior. It stops short of describing the return structure or calculation caveats, but an agent has enough information to invoke it correctly.

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%, so the schema already explains each parameter and its default. The description adds only the general statement that missing inputs use documented defaults, which is consistent with but not richer than the schema. Baseline 3 is appropriate.

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 identifies the tool as an EU drivers' hours calculator and lists the specific outputs it produces: remaining driving today, time before a 45-minute break, weekly and fortnightly remaining driving. This is clear enough to distinguish it from the unrelated sibling tools, though the opening phrase redundantly restates the title.

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?

Usage is implied by 'Run the EU drivers' hours calculator' and the enumerated outputs, but there is no explicit guidance about when to use this tool versus alternatives or when not to use it. Since the sibling tools are not similar calculators, the lack of alternative routing is less harmful, but the description still provides only implied usage guidance.

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