List available services

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

Annotations already declare this is a read-only, idempotent, non-destructive operation, so safety is covered. The description adds genuinely new behavioral context by disclosing that the response payload changes shape depending on whether `domain` is supplied, and that the unfiltered variant is small. Minor gap: it does not say what happens for an unrecognized domain or whether results are cached.

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?

Three short sentences with the core purpose front-loaded, followed by output-shape detail, then the routing rule. The telegraphic 'Without domain / With domain' construction is dense but every clause carries information an agent needs.

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 no output schema, the description does the work of describing the two return shapes, which is the right call, and the single optional parameter is fully covered. It stops short of describing error behavior for an invalid domain, which is the only real gap for a one-parameter lookup tool.

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 domain parameter's example values are already documented in the schema. The description goes beyond that by explaining the semantic effect of the parameter on the result: omitting it yields a compact domain-to-service-names map, supplying it yields full definitions with accepted fields. That meaning is not derivable from the schema alone.

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?

Opens with a specific resource ('Services that can be called') and immediately specifies the two output shapes, so the agent knows this enumerates service definitions rather than states or config. The verb is implied by the name/title rather than stated outright, but the resource and scope are unambiguous. It is clearly distinguishable from siblings like ha_call_service, ha_list_states, and ha_get_config.

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 final sentence names the sibling tool (ha_call_service) and the exact triggering condition: confusion about a service name or its data fields. That is an explicit when-to-use rule with an alternative identified, leaving nothing to inference.

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