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

With no annotations, the description carries the burden of behavioral disclosure. It reveals that image_url is fetched and attached, and banner_svg is rendered to PNG, adding value beyond the schema. However, it does not disclose authentication requirements, side effects, or behavior when both image parameters are provided, which is a gap for a mutating tool.

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 two sentences, front-loaded with the primary purpose and immediately followed by actionable image option instructions. Every sentence earns its place without fluff.

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?

Given the tool has 5 parameters, an output schema, and a large sibling set, the description provides the core workflow and references post_tweet for formatting. It does not mention the npub billing requirement (though the schema does) or what happens if both image_url and banner_svg are supplied, but overall it is sufficiently complete for an agent to invoke correctly.

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 high (80%), so the baseline is 3. The description adds meaningful semantics for the two image parameters by explaining they are 'fetched and attached' and 'rendered to PNG and attached', which goes beyond the schema's simple 'URL of an image to attach' and 'SVG markup string'. It does not explain dpop_token, but that is a minor gap.

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 states 'Post a tweet with a hero banner image to X/Twitter' with a specific verb and resource, clearly distinguishing itself from the sibling post_tweet by the hero banner image addition. It also specifies the two image source options, making the purpose unambiguous.

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 gives clear usage instructions: 'Provide either an image_url (fetched and attached) or banner_svg (rendered to PNG and attached)' and references post_tweet for formatting. It clearly implies this is the image-attaching variant, but does not explicitly state when not to use it or compare it to alternatives beyond the format reference.

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