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

Annotations cover the safety profile (readOnly=false, destructive=false, idempotent=false), and the description adds genuinely new behavioral facts: the 1 GiB cap, that presigned part URLs expire after one hour, that each ETag must be retained, and that the call is refused when a modpack already exists. No contradiction with destructiveHint=false, since the tool only stages an upload.

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?

Front-loads the prerequisite, then the action, return values, and the refusal/alternatives. Dense with parentheticals and colon-chained clauses, but each sentence carries a distinct obligation that an agent needs.

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 multi-step, non-idempotent upload flow with no output schema, the description supplies the return shape (uploadId, key, fileName, parts), the URL lifetime, the ETag retention rule, and the completion handoff. An agent can execute the whole flow from this text plus the schema.

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?

Top-level parameter coverage is 0% and the nested properties only carry schema-level descriptions. The description restates the file-size ceiling and the per-piece PUT flow, but never explains the serverId path parameter or the partCount = ceil(fileSize / 8388608) relationship, leaving that to the schema.

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 and resource ('Begins uploading a Modrinth .mrpack') with a hard size bound (1 GiB). It is clearly separable from startWorldUpload/startAssetUpload and from completeModpackUpload, which the description names as the follow-on step.

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?

Gives an explicit capability prerequisite ('Only for an assistant that can send the user's file with HTTP PUT, such as a coding agent with a shell'), the next tool to call, and an exclusion case ('Refused when a modpack is set') with the two alternative paths (deleteModpack, updateServer).

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