fl_call

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

Goes beyond the annotations by disclosing the return shape ({ok, value} vs {ok: false, error}), that a setter mutates the open project 'as an edit by hand would', that nothing is saved, and that FL must already be running. The destructiveHint=true annotation is consistent with the setter caveat. It stops short of stating whether partial failures or invalid fn names are recoverable, but the added context is substantial.

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 core action and return contract, then layers usage routing and preconditions. Every sentence carries distinct information with no restatement of the name or 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?

With no output schema, the description supplies the return contract itself, plus precondition (FL open), mutation semantics (edit-like, unsaved), and routing to alternatives. Nothing an agent needs before invoking a generic API-dispatch tool is missing.

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 coverage is 100%, so 'fn' (module.function) and 'args' (positional array) are already documented with examples in the schema. The description adds only an illustrative use case ('a parameter name or a mixer level') rather than deeper semantics, so 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?

States a specific verb ('call one function of FL's scripting API') plus the exact return envelope, and positions it against siblings: fl_exec for multiple calls/logic, project_read and project_write for .flp contents. An agent can distinguish this from any other tool in the list without opening a schema.

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 explicit selection criteria: use this for 'a single read or change', fl_exec for several calls or logic, project_read/project_write for anything the .flp holds. It also names a precondition — FL must be open and is not started for this — so the agent knows when the call will fail.

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