proj_variables

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

Annotations already declare readOnlyHint=true and destructiveHint=false, yet the description still adds real behavioral context: how the walk traverses FB/STRUCT nesting, that library-typed variables are collapsed to a single item, and how duplicate names across PLC projects resolve against the connected ADS port. It omits output-size/truncation behavior tied to max_items and max_array, which would have completed the picture.

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 definition in the first sentence, followed by scope and then the collision-resolution edge case. Dense but every sentence carries information; the awkward line wrapping slightly hurts readability but wastes nothing.

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-value explanation is unnecessary, and annotations cover the safety profile. The description covers the semantics an agent needs to call this correctly — what gets flattened, how scope narrows it, and how name collisions resolve — leaving only the three numeric/boolean knobs undocumented.

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 description coverage is 0%, so the description carries the full burden. It explains `scope` well (single program/GVL/FB, or 'PLCproject@name' pinning), but says nothing about `max_array`, `max_items`, or `include_temp`, all of which are non-obvious (array expansion cap, item cap, temp variable inclusion). Partial compensation only.

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 precise verb and resource: enumerate every variable declared in project source, flattened to runtime instance paths by walking programs/GVLs through FB/STRUCT definitions. The example path (MAIN.fbFill.fbValve.bOpen) plus the note about library-typed variables makes the output shape unmistakable. It never names a sibling (e.g. ads_list_symbols, proj_get_code), so differentiation is implicit rather than explicit.

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?

Usage is implied through the parameters: 'scope = one program/GVL/FB to walk instead of all' and the '<PLC project>@<name>' pinning syntax tell an agent how to narrow or disambiguate. But there is no explicit when-to-use/when-not guidance relative to alternatives such as runtime symbol listing or symbol resolution, so the agent must infer the choice.

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