Colour Memory

by app.railway.up.colour-memory-api-production

Get Colour Metrics and Properties

colour_metrics

Read-only

Returns numeric metrics derived from a single display colour: an estimated light reflectance value (LRV) and band, relative luminance, CIELAB lightness, chroma and hue angle, and Bradford corresponding colours under two standard illuminants. It also lists what a hex cannot support, such as thermal performance or a measured LRV. This is one component of colour_passport. Returns isolated numeric values; colour_passport returns the general colour profile that includes them.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "hex_val": "<hex_val>"
    },
    "name": "colour_metrics"
  }
}

Input Schema

Name	Required	Description	Default
`hex_val`	Yes	Hex value e.g. '#8B4513'

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedJun 20, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "description": "Structured JSON response. Shape varies by tool; most return an 'ok' boolean plus a 'result' or 'results' field with the tool's data payload.",
+  "type": "object"
+}

Changed1 schema field changedJun 17, 2026

changedOutput schema / (root)

Previous value: -{
-  "properties": {
-    "error": {
-      "type": "string"
-    },
-    "ok": {
-      "type": "boolean"
-    },
-    "result": {
-      "type": [
-        "object",
-        "array",
-        "string",
-        "null"
-      ]
-    }
-  },
-  "type": "object"
-}New value: +null

AddedJun 2, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations only declare readOnlyHint=true, so the description usefully adds that it reports what a hex cannot support (thermal performance, measured LRV) — a genuine scope boundary an agent would otherwise assume it could query. It also clarifies the return shape as 'isolated numeric values' rather than a profile object. It does not mention determinism, error behavior, or precision/rounding of the derived values.

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?

Front-loaded with the concrete return list, followed by the limitation note and the sibling relationship — a sensible order. The final sentence partially restates the third, since 'returns isolated numeric values' and 'colour_passport returns the profile that includes them' say similar things twice, costing a little tightness.

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?

An output schema exists, so the enumeration of metrics is more than strictly required, and the description covers the main residual need — scope limits of hex-derived metrics and the relationship to colour_passport. For a one-parameter read-only tool this is nearly complete; only error/edge-case behavior is unaddressed.

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

Parameters3/5

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

Schema description coverage is 100% for the single hex_val parameter, including an example, so the schema carries the semantics. The description adds only the implicit notion of 'a single display colour' and does not discuss accepted hex formats, alpha, or named colours. Baseline 3 is appropriate when the schema does the work.

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?

States a specific verb and resource ('Returns numeric metrics derived from a single display colour') and then enumerates exactly which metrics: LRV and band, relative luminance, CIELAB lightness, chroma, hue angle, and Bradford corresponding colours. It also explicitly distinguishes itself from the sibling colour_passport by framing itself as one component of it.

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

Usage Guidelines4/5

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

Gives a clear selection signal: use this for isolated numeric values, use colour_passport for the general profile that includes them. That is a real routing rule rather than vague context. It stops short of explicit exclusions or preconditions (e.g. what input formats are accepted, what to do if the hex is invalid).

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

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