display_image

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

Annotations cover the safety profile (idempotent, non-destructive, closed-world), and the description adds genuinely new behavior: fixed 480x320 rendering, the exact contain-vs-cover visual outcome, and the statefulness of duration 0 meaning "stays until replaced." It omits failure behavior (missing/invalid file, unsupported format) and whether showing an image interrupts other display content.

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?

Four short sentences, each carrying a distinct fact (render size, fit semantics, security boundary, duration semantics), with the core verb and resource front-loaded. Zero filler.

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 3-parameter, no-output-schema tool, the description covers nearly everything an agent needs to invoke it correctly. The remaining gap is error/edge behavior and the interaction with the other display tools, which matters given siblings like clear_display and preview_display exist.

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 0%, so the description must carry the load and largely does: it defines both enum values of `fit` in visual terms and explains the 0 vs 1–86400 semantics of `duration_seconds`. `path` is only partially specified — "local controller image file" implies controller-side resolution but not absolute vs relative paths or accepted formats.

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 specific verb and resource with scope: display a *local* controller image file, resized to 480x320. An agent can immediately tell this is not display_message or speak. It stops short of naming preview_display or clear_display, so the boundary against the preview sibling is left implicit.

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?

"No URL fetching or code execution" is a useful negative constraint that rules out a common wrong call, and the duration rules imply a persistent-vs-temporary usage choice. However, there is no explicit guidance on when to pick this over preview_display or display_message, nor any stated prerequisites such as the file existing on the controller.

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