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

Annotations only tell the agent this is a non-readOnly, non-idempotent, non-destructive, open-world write. The description goes well beyond them by disclosing server-side resource limits, the refusal of 32-bit precision, the reduced size ceiling at 16-bit, and the two-photos-open ceiling — genuine operational constraints an agent must know before calling.

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?

One dense paragraph, front-loaded with the verb and the sibling disambiguation, followed by parameter notes and limits in a sensible order. Every sentence carries information, though the restatement of schema defaults (rgb, white, Background) is mildly redundant.

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?

An output schema exists and the description sensibly just notes the return shape mirrors open_photo rather than re-documenting it. Limits, mode, fill and precision behavior are covered, leaving only the unresolved discrepancy between the prose '32 is refused' and the schema's 32-bit cap as an incompleteness.

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 width/height/mode/fill/name are already fully documented and the description largely restates them. It adds a behavioral note about precision usage, but that note ('32' precision is refused on this server) conflicts with the schema, which documents a 60 MP 32-bit mode — the added meaning is unreliable as a result.

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 a precise verb+resource ('Create a new, empty photo from scratch') and immediately differentiates it from the nearest sibling by naming open_photo as the file-based path. An agent can distinguish this from open_photo, place_image, or make_* tools 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?

Names the alternative ('not from a file: that is `open_photo`') and lays out the conditions under which this tool will or will not work: the workspace pixel limit, '32' precision refused, '16' only up to a smaller size, and a hard cap of 2 open photos. That is explicit when/when-not/alternative guidance rather than inference.

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