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

Goes well beyond the readOnlyHint/openWorldHint annotations: discloses data provenance (ENTSO-E/SMARD via Fraunhofer ISE Energy-Charts), that a licence string accompanies each answer, and the cost model — $0.002 USDC per successful call via x402 across Base/Solana/Arc, with failed calls uncharged. The billing behavior is exactly the kind of non-obvious trait an agent needs before invoking.

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?

One dense paragraph, front-loaded with what the tool returns before provenance and payment terms. Every sentence carries information, though the pricing clause is a long compound sentence that could be trimmed slightly given it repeats no schema field.

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 an output schema present, the description needn't explain return shapes, and it still covers units, defaults, data lineage, licensing and cost. For a zero-required-parameter read tool, an agent has everything needed to select and call 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 coverage is already 100%, so the baseline is 3; the description still adds value by specifying flow units and sign convention (GW, positive = import) and the per-neighbour expansion, neither of which appears in the schema. Zone examples in the description are a subset of the schema's list, so that part is redundant.

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+resource: day-ahead spot prices in EUR/MWh for named European bidding zones, with optional cross-border physical flows. Scope and units are unambiguous. It does not, however, distinguish itself from overlapping siblings such as energy_epex_spot_power_europe or energy_nord_pool_power_elspot, so an agent must infer the difference from the data-source sentence.

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 through defaults (date=today, zone=DE-LU) and the optional flows flag, which tells the agent how to call it minimally. There is no explicit statement of when to prefer this over the EPEX or Nord Pool siblings, and no when-not guidance. Adequate but leaves the routing decision to inference.

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