list_units

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description's 'Read-only.' is largely redundant. The one piece of added context is that it reflects systemd's in-memory view rather than on-disk unit files, but nothing is said about volume of output or how it scales.

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?

Tight and front-loaded: the purpose and read-only nature come first, then one compact line per parameter. No filler sentences, though the parameter block reads as a run-on fragment list rather than clean structure.

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, return values need not be described, and the zero-coverage schema is compensated for by the parameter explanations. The remaining gap is sibling routing against failed_units/list_timers, which an agent would otherwise have to guess at.

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 0%, so the description carries the full burden and largely does: it defines scope's domain ('user' or 'system'), explains state as a LOAD/ACTIVE/SUB state filter, type as a unit type such as 'service', and pattern as a glob over names. It stops short of examples or noting which parameters are optional/defaulted.

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 and resource ('List the units systemd has in memory') and pins it to the underlying command with `--all`. It does not, however, differentiate itself from closely related siblings like failed_units, list_timers, or unit_status, so an agent must infer the boundary.

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?

There is no when-to-use or when-not-to-use guidance, and no mention of the sibling tools that overlap heavily (failed_units, list_timers). The only routing signal is implicit in the parameter descriptions, which is not the same as usage guidance.

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