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

Beyond the read-only annotations, it discloses the return shape (short alt under 125 chars, long description, decorative flag, in-image text, ready attribute), that the image is scaled to 800x800, the model used, and the cost/payment mechanism. This is unusually rich behavioral context for an agent deciding whether and how to call.

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?

Front-loaded with purpose and outputs, and the size is justified by genuinely call-relevant detail (cost, payment, free sample). It is dense and crams the payment mechanics and a full example payload into a single paragraph, but no sentence 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 carries the burden of explaining returns and does so fully, along with inputs, processing, pricing, and workflow. Nothing an agent needs to invoke it correctly 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?

Schema coverage is 100%, so the baseline is 3. The description adds only marginal meaning — the image_url-or-image_base64 either/or, and an example for language ('German') — both of which the schema largely already conveys.

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 — generate alt text for images — and names the accessibility/SEO use case. It also distinguishes itself from the sibling accessibility_check, which 'finds images without alt text', so an agent can route between the two without opening a schema.

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 context (web accessibility per WCAG 1.1.1/BFSG/EAA, and SEO) and an explicit workflow relationship with accessibility_check. It lacks a direct when-not-to-use or alternative-selection statement, but the routing context is strong.

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