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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered; the description adds real domain behavior beyond that: what is optimized, the two comparison baselines (50/50 and all-with-higher-earner), and the legal fact that partners may allocate these items freely in the aangifte. It omits modeling assumptions and limitations, which would push it higher.

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 audience qualifier and then the optimization target; every clause carries information. The main sentence is dense and slightly run-on, but nothing is wasted.

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, no-output-schema optimization tool, the description conveys what the result contains (the split plus savings versus two baselines), which is the essential missing piece. It could say more about assumptions and edge cases (e.g. no Box 3 or no home), but nothing needed to call it correctly is absent.

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 baseline is 3. The description does add a little composite meaning by defining the own-home result as eigenwoningforfait minus mortgage interest, linking woz_value and mortgage_interest_annual, but it adds nothing per-parameter beyond that.

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 ('finds the split') and enumerates the exact resources being split: own-home result, joint Box 3 income and shared deductions, with the optimization goal (lowest total income tax) and comparison baselines. It doesn't explicitly name or contrast a sibling tool, but no other sibling covers partner allocation, so confusion risk is low.

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 opening clause 'For Dutch fiscal partners (married, registered or chosen in the tax return)' gives a clear eligibility condition that tells the agent when this applies. It stops short of stating exclusions or naming alternatives (e.g. single filers should use income_tax_return_netherlands), so it is clear context without routing.

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