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

Annotations already declare read-only, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond that: results are computed on the server from live Fortnox data and aggregated 'over all pages', which tells the agent there is no partial-result or pagination pitfall.

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?

Front-loaded with the resource and its dimensions, followed by a usage example and one provenance sentence. The API documentation URL is slightly incidental but short and harmless.

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?

An output schema exists, so return structure needn't be described; the description covers what is computed, the data source and the all-pages aggregation. Minor gap: it never says what happens when 'date' is omitted (presumably current year) or how from/to_account interact with the default full P&L series.

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 the date (YYYY-MM-DD, selects the year) and the BAS account range for a custom series. The description adds nothing further about parameters, so the baseline of 3 applies.

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 resource and computation: revenue, costs and result per month, current year vs prior year, computed server-side from Fortnox data. The year-over-year, per-month framing distinguishes it in practice from period-P&L siblings like get_profit_and_loss, but no sibling is named explicitly.

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 sample question ('Hur har omsättningen och marginalen rört sig månad för månad i år?') gives a concrete trigger for when this tool is the right pick. There is no explicit when-not guidance or routing to alternatives such as get_key_figures or get_multi_year_overview.

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