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

Annotations only cover the safety profile (readOnly/idempotent/destructive/openWorld); the description adds substantial behavior beyond that: bytes never traverse the API, no serverless size ceiling, 25 MB cap, 1-30 day retention, unguessable key, size signed into the URL, $0.005/call over x402 on Base, prepaid x-credit-token header, and no API key required. That is rich operational context an agent cannot get from the structured fields. One mild tension with readOnlyHint=true exists since the signed slot is intended for a write, but the call itself only mints URLs.

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?

Purpose is front-loaded in the second sentence after a short framing clause, and most sentences carry distinct information (limits, auth, pricing). The opening 'Somewhere to put the file your agent just made' and the 'step every agent hits' sentence are stylized padding that a tighter draft could trim, keeping it just under a 5.

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 an output schema present, return values need no explanation, and the description covers inputs, size/retention limits, auth mechanism, and pricing thoroughly. It is slightly incomplete on edge behavior: the default value for the optional ttlDays beyond the 1-30 range is unstated, and whether repeated calls with identical bytes mint distinct slots (relevant to idempotentHint) is left implicit.

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 the baseline is 3. The description goes further by explaining why 'bytes' is required ('Declare bytes= and the size is signed into the URL') and by tying ttlDays to the 1-30 day retention range, adding meaning the terse schema descriptions do not convey.

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 a specific verb and resource: 'Get a signed upload URL and a retrieval URL for one file, in one call,' and explains the data path (agent PUTs bytes straight to storage). It is unambiguous what the tool returns. It does not, however, distinguish this from plausible siblings like file_publish or file_convert, so it falls short of the 5 bar for sibling differentiation.

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 context is strong and concrete: 'The step every agent hits the moment it produces a report, chart, CSV or build and has nowhere to put it,' which tells the agent exactly when to reach for it. It also gives cost conditions ('no free tier on this tool'). It never names an alternative tool or an explicit when-not-to-use rule, so it stops at a clear 4.

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