List speech-to-text engines

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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds the underlying mechanism ('Filters ha.get_states() for entity IDs starting with stt.*'), which tells the agent the result is derived from current state rather than a registry. It does not add auth/permission or freshness caveats, so it stops short of a 5.

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 core action, then cleanly segmented into Use when / Not for / Returns. Every sentence carries information, though the 'Returns' line partially duplicates the existing output schema, which is mild redundancy in an otherwise tight definition.

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 zero-parameter read-only listing tool with an output schema and full annotation coverage, the description supplies everything an agent needs: what it lists, how it is derived, when to use it, which siblings to avoid, and the shape of the result.

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?

The tool takes zero parameters, so the baseline is 4; there is nothing for the description to clarify or compensate for. The description correctly implies the only 'filter' is implicit (the stt.* prefix) rather than a caller-supplied argument.

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 ('List') and resource ('installed speech-to-text engines'), plus the exact entity namespace ('stt.*') it operates on. It explicitly distinguishes itself from the TTS and wake-word listing siblings by name, so an agent can route without opening any 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?

Provides explicit 'Use when' guidance tied to a concrete downstream need (discovering the STT entity ID to pass to voice_create_pipeline/voice_update_pipeline) and an explicit 'Not for' exclusion pointing to voice_list_tts_engines and voice_list_wake_word_engines. This is the full when/when-not/alternatives pattern.

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