add_sketch_external

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

With no annotations, the description carries the full burden. It usefully discloses a non-obvious behavioral trait: the projected element gets a negative geom index so subsequent constraints can reference it. However, it does not state permission/auth requirements, whether the projection is reversible, or what happens if the referenced geometry changes or is deleted.

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 one-line purpose, followed by necessary ref-format detail and a usage example. The ref paragraph is dense but earns its place given 0% schema coverage. No redundant filler.

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 two-parameter projection tool with no annotations and no output schema, the description covers purpose, ref syntax, behavioral effect, and usage. The sketch parameter itself is left implicit, but it is self-evident from context.

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 must compensate, and it does: it spells out the ref shapes ({handle, edge: tag|'EdgeN'}, face/vertex variants, and {handle, tag} with e_/f_ prefixed tags). This is far more than the schema's bare object type provides.

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 (project), resource (external edge/face/vertex) and destination (into a sketch as construction geometry). This clearly distinguishes it from sibling add_sketch_geometry, which adds sketch-native geometry rather than projecting upstream edges.

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?

Provides a clear when-to-use rationale and a concrete example ('a hole 5mm from a tagged edge that survives pad-length edits'), which tells the agent this is for anchoring sketches to upstream geometry. It stops short of naming an explicit alternative or exclusion condition.

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