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

Annotations already declare this is a non-destructive, non-open-world write, so safety is partly covered. The description adds a substantive rule beyond the annotations — never fabricate stock/placeholder/Unsplash URLs and instead prompt the user — which genuinely shapes agent behavior. It does not mention permissions or insertion side effects, keeping it below a 5.

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?

Three sentences, front-loaded with the action followed by the sourcing constraint. The second and third sentences overlap somewhat (avoid inventing URLs / ask the user for a real image), so it is slightly more verbose than strictly necessary.

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 11-parameter insert tool with no output schema, the description covers purpose and the critical behavioral guard, while the schema covers all parameters. Nothing essential is missing, though positioning/return expectations are left entirely to the schema.

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% across all 11 parameters, and the schema itself carries strong semantics (e.g., 'after' noting that omission is 'usually wrong', 'position' enum semantics). The description adds no parameter-level detail beyond that, so the baseline 3 applies.

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 opens with a specific verb+resource ('Insert an image element'), so an agent immediately knows the operation. It does not explicitly contrast itself with nearby siblings like editor_insertPictureChoiceQuestion or editor_insertEmbedded, but the resource is distinct enough that confusion is unlikely.

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?

It gives clear preconditions for use ('a user uploaded' image or 'a URL the user explicitly provided') and an explicit negative case (no real image → ask the user to upload or paste a URL). It stops short of naming alternative tools, but the when-to-use guidance is concrete.

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