plc_list_variables

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds only that preserved attributes are included in the listing, which is modest extra value; it says nothing about pagination behavior, result ordering, or whether transaction_id gives a transactional view.

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?

Two short sentences, front-loaded with the operation and followed by the scope constraint; no filler. The terseness borders on under-specification, but nothing written is wasted.

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?

An output schema and read-only annotations reduce what the description must explain, and the scope semantics are covered. For a six-parameter tool with only a third of its schema described, however, the unexplained query and transaction_id parameters leave real gaps an agent must resolve by trial.

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 only 33%, so the description must carry weight, and it clarifies only 'scope'. The 'query', 'transaction_id', and 'project_id' parameters get no explanation, leaving the agent to guess whether 'query' filters by name and what transaction_id does for a read.

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 ('declarations' for global or POU-local scope, plus preserved attributes). An agent can distinguish it from plc_list_pous or plc_list_data_types by the declaration focus, though the description never names those siblings or says explicitly that these are variable declarations.

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 second sentence tells the agent what values 'scope' takes ('global' or a POU ID), which implies how to choose global vs. POU-local listing. There is no explicit when-to-use vs. alternatives guidance, no mention of pairing with plc_list_pous to obtain a POU ID, and no exclusions.

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