tv_drawing_add_horizontal_line

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

Annotations already mark the tool as destructive. The description adds 'Experimental' and 'Best-effort' as additional behavioral caveats, which provides some value beyond annotations. However, it doesn't detail failure modes, side effects, or what 'best-effort' means in practice.

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?

The description is exceptionally concise: one sentence with the action front-loaded, followed by a two-word caveat. Every word serves a purpose, and the 'Experimental' and 'Best-effort' tags are essential context. No wasted content.

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 low-complexity tool with one optional parameter and annotations, the description is largely sufficient. It states the core action and adds a reliability caveat. It doesn't explain return values or error behavior, but given the simplicity and that no output schema exists, this is acceptable.

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 schema fully covers the only parameter (yPct) with a clear description of its semantics (fraction of chart pane, default 0.5). The tool description's phrase 'chosen Y-position' mirrors this but adds no new information, so the baseline of 3 applies.

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?

The description clearly states 'add a horizontal line at a chosen Y-position on the chart pane.' This uses a specific verb (add), identifies the resource (horizontal line on chart pane), and differentiates from sibling drawing tools like trendlines and rectangles.

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 description gives no guidance on when to use this tool versus alternatives. It mentions 'Experimental' and 'Best-effort' but these are reliability warnings, not usage context. There's no mention of when a horizontal line is preferred over other drawing tools, and no exclusions.

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