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

With only a title annotation, the description still carries real behavioral weight: it names the available models and their limits (recraft ≤2048px, topaz factor 2–6), discloses that credits scale with output megapixels, and notes var2 share links are auto-resolved. It never says the job is asynchronous or how results are fetched, which is the one notable omission for a generation 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?

Front-loaded with the two core operations, then candidate triggers, then disambiguation. Dense and slightly overloaded with parenthetical synonyms and arrow chains, but nearly every clause routes or constrains a decision rather than padding.

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 5-parameter async image tool with no output schema, the description covers types, models, credit implications, and input URL forms, with the webhook delivery contract documented in the schema. The missing piece is that the result is retrieved asynchronously (presumably via var2_get_image_result), leaving the post-call lifecycle implicit.

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 coverage is 100%, so baseline is 3, but the description adds value the schema lacks: it enumerates the valid model names and their resolution constraints, and cites the natural-language triggers that map to each type value. Defaults and factor range largely restate the schema, keeping it out of 5 territory.

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?

States two specific operations (background removal and upscaling) on a specific resource (an existing IMAGE), and explicitly disambiguates from siblings by media type: audio edits go to var2_create_audio, video to var2_create_video/var2_join_videos, stylistic edits to var2_create_image. An agent can select it without opening any schema.

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?

Gives explicit conditions for use (upscale cues like 'sharper', 'enhance', '2K/4K/8K'; cut-out for background removal), states the closed type set ('no other type exists'), and routes alternative intents to the correct sibling tools. When-not-to-use is covered via the media-type exclusions.

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