select_by_index

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

With no annotations, the description carries the full burden and does reasonably well: it discloses that selection replaces the current selection unless 'extend' is set, and that the return value reports a selected count plus mesh totals. It omits any note on permission/context requirements or behavior when indices are invalid (beyond the stated constraint).

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 Args/Returns in a scannable format; each parameter line earns its place. The 'no operator, no viewport, no guessing' line is mildly promotional but does convey that selection is deterministic rather than interactive.

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 4-parameter selection tool with no annotations and 0% schema coverage, the description covers the missing pieces: parameter meanings, replace-vs-extend behavior, and input constraints. The Returns section is somewhat redundant given an output schema exists, and no failure behavior is described, leaving a small gap.

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 all four parameters must be explained here, and they are: object_name, element with its enum values, indices with a non-negativity/in-range constraint, and extend with its add-vs-replace semantics. This fully compensates for the undocumented schema.

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 ('Select specific vertices, edges or faces by index') and contrasts itself against interactive/operator-based selection, which helps separate it from the crowded select_* family. It does not explicitly name sibling alternatives like select_by_axis, select_similar, or select_all_geometry, so sibling differentiation is only partial.

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?

Gives a real workflow trigger: analyze_mesh_quality reports sample indices per defect, and this tool is how to act on them. That is concrete when-to-use guidance. It stops short of saying when NOT to use it versus the other selection tools.

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