Sign file URL

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

Annotations already declare the write/destructive, non-idempotent, open-world profile, so the bar is lower. The description still adds real value: the ACL bypass behavior, the 7-day TTL ceiling, and the explicit `assets:read` permission requirement. It does not, however, note that the signed URL is written to a file rather than returned.

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, front-loaded sentences: purpose first, use case second, constraints/auth last. No filler, every sentence earns its place.

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 7-parameter tool with a nested payload object, mutually exclusive body inputs, a required output_file, and no output schema, the description covers only purpose, TTL, and auth. It never explains where the signed URL goes or how the payload/payload_file/flat-flag union works, leaving the schema to carry those semantics.

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 schema already documents all 7 parameters including expiration_seconds' max. The description's 'valid for expiration_seconds (up to 7 days)' merely restates the schema, adding no new format or constraint meaning.

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+resource ('Creates a signed URL that grants temporary access to a fal CDN file') and adds a distinguishing capability ('regardless of its ACL'). This clearly separates it from ACL-management siblings like get_storage_file_acl / set_storage_file_acl, though it never names an alternative explicitly.

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?

'Useful for sharing access-restricted files' gives one implied use case but no when-not conditions, prerequisites, or named alternatives. The agent can infer usage but must reason about it rather than being told.

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