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

The description discloses behavior beyond the annotations: it copies static_urls, is instant/free/no credits, idempotent, and requires a rendered source. Since readOnlyHint=false aligns with the mutation action, there is no contradiction. The added detail fully informs the agent of operational side effects.

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 description is compact and well-structured: first sentence states the core action and benefit, second provides usage context with a counterexample, and third covers prerequisites and idempotency. No redundant phrases; every sentence adds value.

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?

Given the tool's moderate complexity, the description fully covers what it does, when to use it, prerequisites, behavioral effects, and idempotency. The absence of an output schema is acceptable because the purpose is a simple copy operation and the outcome is implied by the description.

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 covers 67% of parameters with examples (from_cell and to_cell). The description adds the mechanism 'Copies the source's static_urls onto the target', which explains the relationship between parameters and the effect. session_id is left to inference but is a common field; the description partially compensates for the gap.

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 and resource: 'Copy an image that already exists on one output onto another cell.' It immediately clarifies the operation's purpose and distinguishes it from niche_render_image_card by contrasting cost and outcome, making the tool's intent unmistakable.

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?

Explicit usage guidance is provided: 'Use this when the user wants "the same image" on a second surface... instead of niche_render_image_card.' It also states prerequisite conditions (both cells must exist, source must have rendered image) and points to niche_add_output as a fallback, offering both when-to-use and when-not-to-use context.

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