Create or update a runtime entity group

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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false), but the description adds real context beyond them: the group is not written to groups.yaml, it disappears on restart or YAML reload, it forwards to group.set, and it returns a specific error payload without calling the service when entities is combined with add/remove. The one gap is that replacing the entire member list via `entities` sits awkwardly beside destructiveHint=false, though the replacement semantics are at least disclosed.

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 and sectioned, but repetitive: the persistence caveat and the files_write_config_file alternative appear twice, and the entities/add_entities/remove_entities exclusion is stated three times (service-call paragraph, Errors, Limits). Trimming the duplication would lose no information.

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 7-parameter mutation tool with an output schema already present, the description covers the essentials an agent needs: mutation semantics, persistence lifecycle, valid parameter combinations, error behavior, and the correct alternative for persistent groups. Nothing material is missing.

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%, so the baseline is 3, but the description adds value by enumerating exactly which fields are forwarded to group.set and by spelling out the failure contract for the entities vs add_entities/remove_entities conflict. Minor wrinkle: it refers to the `all` parameter while the schema names it `all_entities`, which could momentarily confuse mapping.

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 ('Create or update an old-style group.* entity at runtime') and immediately draws the boundary against adjacent capabilities, explicitly noting it does not create light/switch/cover group helpers. Combined with the sibling set (automations_list_groups, automations_remove_group, helpers_*), an agent can place this tool precisely without opening the schema.

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?

Gives an explicit when-to-use (runtime group that need not survive restart) and when-not ('Not for: a group that survives a restart'), naming the concrete alternatives — groups.yaml via files_write_config_file or a Group helper. It also states the mutually exclusive parameter combinations, so the agent knows how to shape a valid call.

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