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

With no annotations, the description carries the full burden and does disclose meaningful traits: authentication is mandatory, the call is metered ('One credit'), the return is a hosted URL, and there is a limitation ('Does not return a free hotlink'). It omits failure behavior, whether credits are spent on error, and supported page requirements, so it is good but not complete.

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?

Three short sentences, each earning its place: purpose and return value first, then the auth/cost constraint, then the negative caveat. Nothing is padded or redundant.

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 no annotations and no output schema, the description reasonably covers purpose, auth, cost, and return format. It still leaves gaps: no distinction from render_og_image, no explanation of the four styling parameters, and no note on error or credit-refund behavior, which matters for a metered call.

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 only 33% across 6 parameters, so the description would need to compensate. Instead it only reiterates url and api_key (both already documented in the schema) and says nothing about font, size, theme, or layout, whose enums are unlabeled and offer no guidance on defaults or effect.

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 gives a concrete verb and resource ('Build a hosted Open Graph card from a public page') and names the extracted fields, so the agent knows exactly what it produces. It does not, however, distinguish itself from the sibling 'render_og_image', which sounds like the same operation, leaving the agent to guess which to call.

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?

It supplies real invocation constraints (requires api_key, costs one credit, no free hotlink) which guide usage, but it never states when to prefer this tool over render_og_image or og_pricing. The routing decision between the near-identical siblings is left entirely to inference.

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