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

Consistent with readOnlyHint=true, and it goes well beyond the annotation by disclosing cost (free), the exact outputs (two PNGs plus a summary), the conditional nature of the envelope render, and what the summary flags: missing fields, overflowing text, oversized address. That is genuine behavioral context an agent cannot get from the annotations.

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 front-loaded sentence that names the render action first, then the outputs, then the readiness summary. It is dense with clauses but each one carries distinct information; the parenthetical list of failure modes is slightly heavy but not 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 takes on the burden of describing return values and does so thoroughly, including the conditional envelope PNG and the contents of the readiness summary. Nothing an agent needs to call and interpret this tool is missing.

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?

Only one parameter and schema description coverage is 100%, so the schema already explains that 'id' is the postcard ID with an example format. The description adds no additional meaning about the ID, which is acceptable at this coverage level but is the baseline, not a value-add.

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 ('Render') and resource ('a postcard as the customer will receive it') and enumerates the concrete artifacts produced: a card PNG, an envelope PNG, and a readiness summary. An agent knows exactly what this does without opening the schema, and it is clearly distinct from data-fetching siblings like get-postcard-tool.

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?

Gives clear usage context: 'Free; works for drafts and sent postcards', and notes the envelope render requires the address, recipient, and font to be set. It implies the pre-send check use case but never explicitly names an alternative (e.g., get-postcard-tool) or states when not to use it.

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