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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so safety and mutability are covered. The description adds genuinely new context — which suppliers are covered and that each entry states which homes are eligible — but says nothing about result size, pagination, or the shape/format of a tariff identifier.

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?

It is a single sentence with no filler, but that sentence is dense and hard to parse, stacking an em-dash aside, a parenthetical cross-reference, and a trailing clause ('each saying which homes can have it'). Splitting it into action plus direction semantics would read far better without adding length.

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 one-optional-parameter, read-only listing tool with no output schema, the description covers what the tool is for and the import/export split, which is the essential part. It stops short of describing what a returned entry looks like — particularly the identifier format that feeds the `tariff` parameter — which is the one thing an agent most needs from a value-listing tool with no output schema.

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% and the enum already documents `import` versus `export`, so the baseline is 3. The description goes further by explaining what `direction=export` actually yields (export tariffs used with get_prices' export mode), which adds downstream meaning beyond the one-word enum values.

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 a specific resource (time-of-use and standard tariffs from Octopus, EDF, E.ON Next) and scopes it as the set the `tariff` parameter accepts, which distinguishes it from siblings like get_prices that consume those values. It is clear what the tool enumerates, though the verb ('list') is only implied and the sentence is built around the downstream parameter rather than the tool's own action.

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 rather than stated: by saying these are the tariffs 'the `tariff` parameter accepts', it suggests calling this before get_prices, and it notes the export variant is for get_prices/`export`. However, it never explicitly says when to call list_tariffs instead of get_prices, nor any exclusions or preconditions.

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