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

Annotations already declare this is a non-readonly, non-idempotent, non-destructive operation, and the description adds real value on top: it returns an edit link alongside the interactive card, caps input at 128x128 pixels / 256 colours, and states that the user's edits persist to the edit session. The only gap is that it doesn't explain how the edit session itself is created or returned.

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 source-selection rule and return-link behavior are front-loaded and useful, but the long middle feature catalogue ("layers, selection and move, line/rectangle/ellipse, mirror painting, brush sizes, animation frames with onion skin and playback, palette tools") reads as marketing copy that adds little to tool selection.

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 an 8-parameter, no-required-args tool with nested `art` and no output schema, the description covers the input source options, hard limits, and what is returned (an edit link). It is nearly complete; only the relationship to the sibling editor tools is left out.

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 already 100%, so the baseline is 3; the description goes beyond it by framing the eight parameters as mutually exclusive source options with "none" meaning a blank canvas, which the schema alone does not convey. It also restates the size/colour limits that are only partly encoded in the schema.

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?

Opens with a specific verb+resource ("Opens a sprite in SpriteForge's full pixel editor") and enumerates the capabilities that make it the *full* editor, which implicitly distinguishes it from the lighter `open_sprite_in_editor` sibling. However, it never names or contrasts with that sibling or `open_tileset_editor`, so an agent must infer the difference.

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?

"One source at most: session_id, asset_id, png_base64, art, or none for a blank width x height canvas" is an explicit, actionable selection rule that tells the agent exactly which input path to pick. It stops short of stating when to prefer this tool over `open_sprite_in_editor` or `load_art`, so it is clear context without exclusions.

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