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

Beyond the readOnlyHint annotation, the description discloses the exact model (Machado, Oliveira & Fernandes 2009), the fixed severity (1.0), the working colour space (linear sRGB), the clipping flag, and the caveat that this is a model prediction, not individual perception. This is rich behavioural context for a simulation tool.

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 front-load the primary behaviour and then add only high-value constraints and caveats. No filler or repetition of the schema.

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 single-parameter readonly simulation with an output schema present, the description covers the input domain, model, scope, failure/edge behaviour (clipping flag), and interpretation caveat. There are no obvious gaps that would prevent an agent from calling it correctly.

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?

Input schema already fully documents hex_val with an example, so schema_description_coverage is 100%. The description confirms the hex input by saying 'simulated hex values' but adds little beyond the schema for parameter semantics.

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?

Description opens with a specific verb and object: 'Return simulated hex values' for three named colour-blindness variants, tied to a named model. It also states exclusions that stop an agent confusing it with accessibility_check or accessibility_matrix.

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?

The description clearly scopes when this tool applies: full-severity protanopia/deuteranopia/tritanopia only, and explicitly says anomalous trichromacy and partial severities are not simulated. It does not name an alternative tool, but the exclusion boundaries are explicit enough to guide selection among the accessibility siblings.

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