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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so safety is covered. The description adds real value beyond that: brightness magnitude scaling, label handling, and the cost/endpoint lines. It stays silent, however, on output shape and on the fact that the options.format enum defaults to 'json' despite the SVG title.

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 tight sentences with the projection method front-loaded, followed by a compact bracketed metadata block. Every element is short and none is redundant padding, though the endpoint line duplicates information the platform likely already carries.

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 an 8-parameter tool with nested objects and a low description coverage rate, this is thin: observer position and altitude-cap parameters that materially change the rendering are never mentioned, nor is compact mode (fields/precision). The existing output schema does relieve it of explaining return values.

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?

With 8 parameters and only 25% schema description coverage, the description must compensate and largely does not. It maps loosely to the point fields (RA/Dec, magnitude), but observerLatDeg, zenithDecDeg, capAltitudeDeg, precision, and the whole nested options object (theme, size, format, showAspects) receive no explanation.

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 gives a specific rendering operation ('Stereographic projection of caller-supplied points (RA/Dec)') plus the two rendering behaviors it implements (magnitude scaling, labels). It clearly identifies the resource and method, but does not differentiate itself from the many render_* siblings (cosmogram, eclipse_path, bi_wheel, etc.).

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?

There is no statement of when to use this tool versus alternatives, no prerequisites, and no exclusions. The '[Required: points]' and '[Cost: 10 credits]' lines are operational metadata, not usage guidance, so an agent gets no help deciding between this and sibling renderers.

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