Sign file URL

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

Annotations already declare destructiveHint=true, readOnlyHint=false and idempotentHint=false, so the safety profile is covered. The description adds genuinely new context beyond that: the assets:read permission requirement, the authentication requirement, and the 7-day validity ceiling on the generated signature. It never explains why a signing operation is flagged destructive (the required output_file write), which is the one notable gap.

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 blocks, front-loaded with the core action and scope before the validity constraint and auth note. Every sentence carries information; only the parenthetical restatement of the 7-day limit is mildly redundant with the schema.

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 and no output schema, the description covers the essentials: what it produces, its ACL-bypassing behavior, validity window, and auth/permission requirements. It leaves the output_file contract and the destructive write side-effect implicit, relying on the schema to convey them.

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 url, account, confirm, payload, payload_file, output_file and expiration_seconds are all documented in the schema itself. The description only echoes the expiration_seconds 7-day cap, adding nothing about the payload vs. flat-flag mutual exclusion or the confirm flag's meaning. Baseline 3 applies when the schema does the heavy lifting.

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 ('Creates a signed URL') and resource ('fal CDN file') plus the key behavioral distinction 'regardless of its ACL'. This clearly separates it from siblings like get_storage_file_acl and set_storage_file_acl, which inspect or mutate ACLs rather than mint access credentials.

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 a concrete when-to-use context, which is the main reason an agent would pick this over the ACL siblings. It does not name an explicit alternative or state exclusions (e.g., that ACL changes should use set_storage_file_acl instead), so it stops short of full routing guidance.

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