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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true, so the safety profile is clear. The description adds valuable context beyond annotations: it explains the source (DSCOVR EPIC camera), the nature of images (daily natural color photos), and the vantage point (Lagrange point L1). No contradictions.

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?

The description is a single, front-loaded sentence of about 25 words. Every part is meaningful, with no redundant or extraneous information. It efficiently conveys the core purpose and key context.

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?

Given the tool has an output schema (not shown but present), the description does not need to detail return values. With one optional parameter and clear purpose, the description covers the essential context for selecting and using the tool. Minor gap: no mention of how images are returned or any pagination, but not critical for a simple read-only tool.

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 description coverage is 100%, and the single parameter 'date' is well-documented in the schema with its format and default. The description does not add additional meaning beyond what the schema already provides, only repeating the tool's purpose. Baseline 3 is appropriate.

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 clearly states the verb 'Get' and the resource 'full-disc Earth images', specifying the DSCOVR satellite EPIC camera, daily natural color photos, and location (Lagrange point L1). This distinguishes it from other NASA tools like 'nasa.asteroids.feed' which targets asteroids.

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 implies usage for retrieving Earth images from DSCOVR but does not explicitly state when to use this tool over siblings such as 'nasa.astronomy.apod' or 'nasa.media.search'. No alternatives are mentioned, and there is no contextual guidance on when not to use it.

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