Check a caption

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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description is consistent with them. It adds genuinely useful behavior detail beyond the annotations: the concrete thresholds enforced (2,200 chars, 30 hashtags, 20 mentions) and that the preview applies the template with publish-time fidelity, though it says nothing about what the check returns on failure.

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?

A single dense sentence that front-loads the validation behavior before the preview behavior, with no filler. The parenthetical limit list is efficient, though the sentence is long enough that the preview capability could be separated for scannability.

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 simple read-only two-parameter tool the inputs are adequately framed, but with no output schema the description should say what a check yields (violation list? pass/fail? rendered preview string) and what happens if template is absent. Those gaps matter because the tool's whole value is in its result.

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 0% for two parameters, so the description must carry the load. It clarifies the optional template parameter's effect ('applied exactly as it will be published') but never states what happens when template is omitted, nor any caption format/length expectations beyond the limit itself.

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 ('Checks') plus a specific resource ('a caption') and enumerates the exact rule sets applied (Instagram limits, craft rules) and the preview behavior. An agent can distinguish it from generate_caption or critique_cover without opening any 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?

Usage is only implied: 'previews it ... exactly as it will be published' suggests a pre-publish validation step, but the description never says when to call this versus generate_caption or critique_cover, nor any preconditions (e.g. must a template exist first).

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