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

With annotations already covering safety (readOnlyHint=false, destructiveHint=false), the description adds crucial operational semantics beyond them: a signed-URL handshake, exact PUT requirements with headers, URL/file expiry, one-file-per-upload immutability, CDN caching for up to 4 hours, and the rule never to reuse an earlier upload_url. These are non-obvious behaviors an agent could easily get wrong.

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 purpose and size threshold, then the operational workflow, then consumption targets. Although long, every sentence carries distinct operational value—expiry, immutability, header requirements—and the curl example is a compact concrete instruction rather than filler.

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?

No output schema is provided, and the description explains the relevant returned fields (upload_url, headers, upload_url_expires_at, url, url_expires_at) and how they behave. Combined with the PUT workflow and consumer tools, an agent has everything needed to call it 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 100%, so the content_type enumeration and meaning are fully documented by the schema. The description adds only indirect context via the curl example showing a matching Content-Type header. That is marginal beyond the schema, so the baseline 3 applies.

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?

Starts with a specific verb and resource: 'Get a signed URL to upload a local file'. Immediately qualifies scope (too large for a data URL, over ~3 MB, up to 100 MB) and the file kinds supported. An agent can tell this apart from generate, create_character, and create_reference, which consume the result rather than create uploads.

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?

Explicitly states the precondition ('Only for a file on a machine where you can run commands: this server cannot read files attached to the chat') and the size-based reason to choose this over a data URL. It names the downstream tools that consume the returned URL (generate, create_character, create_reference, estimate_cost), giving clear routing guidance.

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