hcl-mcp

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colored_sky

Generates a colored Perez sky and sun radiance definition for Radiance lighting simulations, supporting spectral or luminance modes and customizable solar position.

Instructions

Generate a colored Perez sky+sun Radiance definition.

mode 'spectra' (per-channel spectral scaling, runs gendaylit) or 'luminance' (Radiance -C built-in coloring, 3-channel only, pure emit). irrad_mode 'W' (direct+diffuse) or 'E' (global). diffuse_channels/direct_channels: 3 or 9 channel values (from spd_to_channels); ignored in luminance mode. lon is standard signed / EAST-positive (Seattle = -122.3, Athens = 23.73), matching raw EPW.

SOLAR POSITION. By default the sun is derived by gendaylit's own ephemeris from month/day/hour + lat/lon/utc, and hour is read as a WALL-CLOCK instant. spectral_sky_from_epw's hour is a different thing — an EPW hour-ENDING label, whose geometry is evaluated at the mid-interval instant (hour - 0.5) because the row's DNI/DHI are averaged over the preceding hour. Passing the same integer to both therefore puts the spectrum and the traced sky half an hour (7.5 deg of diurnal arc) apart, with no error raised.

To keep them on one instant, pass that record's geometry through here VERBATIM: sun_zenith_deg = record["geometry"]["zenith_deg"] sun_azimuth_deg = record["geometry"]["azimuth_deg"] Both are required together; supplied, they emit gendaylit's -ang form and make the record's position authoritative for the traced geometry. Omitted, behaviour is unchanged.

Input Schema

TableJSON Schema

Name	Required	Default
`day`	No
`lat`	No
`lon`	No
`run`	No
`utc`	No
`hour`	No
`mode`	No	spectra
`name`	No	sky
`globl`	No
`month`	No
`direct`	No
`diffuse`	No
`work_dir`	No
`irrad_mode`	No	W
`channel_type`	No
`sun_zenith_deg`	No
`direct_channels`	Yes
`sun_azimuth_deg`	No
`diffuse_channels`	Yes

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 9, 2026

TDQS

A4.7/5.0

Behavior5/5

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

With no annotations provided, the description carries the full burden and does so admirably. It discloses how mode affects execution (spectra runs gendaylit, luminance uses Radiance -C built-in coloring), how hour is interpreted as a wall-clock instant, and the subtle half-hour offset issue. It also notes that diffuse_channels/direct_channels are ignored in luminance mode.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but not wasteful; every sentence adds technical substance. It front-loads the core purpose and modes, then dedicates a focused paragraph to the solar-position gotcha. It could be slightly trimmed but is well-organized.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a complex tool with 19 parameters, the description covers the most critical behavioral aspects and the main integration pitfall. The output schema exists, so return values are not needed. Minor omissions like the exact role of channel_type and globl prevent a 5, but overall it is sufficiently complete for correct usage.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Despite 0% schema description coverage, the description adds meaning to several key parameters: mode, irrad_mode, lon (explicit EAST-positive), hour (wall-clock vs EPW hour-ending), and the sun angle pair. However, it does not explain all 19 parameters (e.g., channel_type, globl, direct, diffuse, work_dir), leaving some to be inferred from context.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a clear verb-resource statement: 'Generate a colored Perez sky+sun Radiance definition.' It then distinguishes itself from the sibling spectral_sky_from_epw by explaining the hour semantics difference, so an agent can tell them apart without inspecting schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives explicit guidance on when to use the default ephemeris versus passing sun_zenith_deg and sun_azimuth_deg, and it explains the alignment problem with spectral_sky_from_epw, including a concrete example of how to pass geometry verbatim. This is far beyond a generic 'when to use' note.

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