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

With no annotations provided, the description takes on the full burden of behavioral disclosure. It does this thoroughly: the image is never re-encoded, existing metadata of the same kind is replaced rather than duplicated, calls are paid per success, the first attempt returns HTTP 402 with the price, and failed calls are not charged. These are meaningful, non-obvious behaviors an agent needs to operate correctly.

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 three sentences with no filler. The primary purpose is front-loaded, followed by key behavioral guarantees and payment mechanics. Every sentence earns its place, and the structure lets an agent quickly grasp the tool's core function before reading details.

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?

For a tool with 7 parameters, no annotations, and no output schema, the description covers formats, re-encoding behavior, replacement semantics, and payment flow. The only notable gap is the exact representation of the returned 'modified image' (e.g., base64, binary, or URL) and more detailed non-402 error behavior. Since no output schema exists, a slightly more explicit return format would make it fully complete.

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 description coverage is 100%, so the schema already documents every parameter clearly. The description adds general context about SEO metadata, replacement semantics, and supported formats, but it does not add meaning to individual parameters beyond what the schema provides. A baseline of 3 is appropriate since the schema carries the parameter-level load.

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: 'Write SEO metadata into a JPEG, PNG or WebP image and return the modified image.' It clearly states the action, supported formats, and return behavior, leaving no ambiguity about what the tool does. There are no sibling tools to differentiate against, so this fully satisfies purpose clarity.

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?

The description implies when to use the tool—when you need to write or replace SEO metadata in supported image formats—but does not explicitly state usage contexts, prerequisites beyond image format, or exclusions. It adds the payment flow as a practical usage condition, but there is no guidance on when not to use it or what alternatives exist. This is adequate but not explicit.

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