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

With no annotations, the description carries the full burden and delivers an exceptionally detailed disclosure: deterministic layout with exact text fidelity, beat-by-beat reveal semantics ('text never shifts'), script/emoji rendering limits, signed-URL expiry (2 h, 'image is not inlined'), cap enforcement 'refused BEFORE payment', and Lightning pricing. This is a model disclosure profile for a paid render tool; there is no contradiction with any structured data.

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?

Every clause earns its place: core capability first, then determinism, use cases, reveal behavior, font coverage, return shape, caps, and pricing — in that order. For a tool with 20 parameters, five variants, no annotations, and no output schema, the length is warranted density, not bloat. There is no filler or boilerplate.

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?

Despite having no output schema and no annotations, the description covers the return shape ({ url, width, height, format, mime, expires_in_seconds }), the fetch-the-URL behavior, the payment prerequisite and price, validation caps, and font limits. An agent could invoke this tool correctly with only the description plus the already-descriptive schema; the only minor ellision is error-handling for invalid/expired payments.

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 the baseline is 3, and the description genuinely adds beyond the schema by composing parameters into patterns ('Lists and comparisons REVEAL one beat at a time (revealed:N / show_right:false)') and by tying paymentId to the create_payment prerequisite. The count/length caps are already encoded in the schema (1-6 items, 1-3 lines), making the description's cap mention partly redundant, so it stops short of a 5.

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'), a specific resource (a typographic card with five named variants: headline, versus, list, stat, quote), and concrete output constraints (PNG/JPEG at 1920x1080 or 2560x1440). The 'no AI model... which no image generator can promise' line explicitly distinguishes it from sibling image-generation tools, so an agent can select it correctly without inspecting schemas.

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?

Names concrete use cases ('video title cards and slides, thumbnails, quote cards and social posts') and the required companion flow ('Requires create_payment with toolName='render_card''). The determinism contrast with image generators gives implicit when-to-use guidance, though no sibling tool is explicitly named as the alternative and there is no explicit when-not-to-use statement.

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