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

Annotations already establish readOnlyHint=true and destructiveHint=false, so safety is covered. The description still adds genuinely useful behavior: a video path yields the first frame rather than an error or a video, and the output is downscaled to max_edge. That is real context beyond the structured fields.

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?

A single tight sentence with the core action front-loaded and the parenthetical edge case placed immediately after it. Nothing is wasted.

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?

With no output schema, the description's claim that it 'returns an image' leaves the return encoding (inline image content vs. URL vs. file reference) unspecified, which matters for a binary-returning tool. It is otherwise adequate for a 3-parameter read tool.

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 path, max_edge (default 1024, range 256-2048) and project_id are already documented in the schema. The description only re-references max_edge and the video-first-frame behavior, adding no format or syntax detail beyond the schema baseline.

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 ('Returns an image from the project') plus a non-obvious capability: extracting a video's first frame. An agent can distinguish it from text-reading siblings like composer_read_file and from mutation siblings like composer_edit_image, though it never names an alternative explicitly.

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?

There is no when-to-use or when-not-to-use guidance, no prerequisites (e.g. that project_id must come from composer_project_create), and no mention of alternatives. Usage is only inferable from the verb.

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