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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent write. The description goes beyond them by disclosing the required 'attachments:write' scope (a real auth requirement) and the exactly-one-parent invariant, which the agent needs to avoid a failed call. It stops short of stating failure behavior when zero or multiple parents are supplied.

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, all load-bearing: what it creates, the parent-linkage constraint, and the scope requirement. Nothing redundant and the most important constraints are front-loaded.

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 needed, 100% parameter coverage, and annotations carrying the safety profile, the description supplies the remaining essentials (scope, parent invariant). Its only real gap is not clarifying the relationship to the file-upload siblings so the agent understands where file_url must originate.

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 every one of the 10 parameters is already documented in-schema, including the 'exactly one parent required' notes on each parent ID. The description reinforces the mutual-exclusion rule but adds no syntax or format meaning beyond the schema, making the baseline 3 correct.

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?

Names a specific verb (Create) and resource (attachment record) and enumerates the four allowed parent types, so the agent knows exactly what is being produced. It does not, however, differentiate itself from the confusable siblings create_upload_url and upload_file, which also deal with file ingestion, so sibling disambiguation is incomplete.

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 constraint 'Exactly one parent ID must be provided' gives a clear precondition for a successful call, which implies the usage context. But it offers no explicit when-to-use guidance and never routes the agent to alternatives such as upload_file or create_upload_url for getting the file into storage first, leaving the workflow inference to the agent.

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