set_expression

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

Annotations already declare idempotentHint=true and destructiveHint=false, so the description need not cover repeatability or safety classification. It adds useful behavioral context beyond annotations: per-frame evaluation and a regex pre-flight rejecting forbidden Python/TCL calls.

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 purpose and behavior, then provides examples and restrictions. The Args section repeats the schema descriptions verbatim, which is slightly redundant, but the overall structure is efficient and readable.

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 setter tool with no output schema and full schema coverage, the description covers purpose, expression format, security behavior, and parameter meanings. It could mention clearing expressions via the sibling clear_expression, but otherwise an agent has enough 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 baseline is 3. The description adds meaning beyond the schema by giving concrete TCL expression examples (frame, frame/24.0, sin(frame*0.1)) and noting security restrictions on expression content.

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 and resource: 'Set a TCL expression on a knob,' and clarifies per-frame evaluation. This clearly distinguishes it from sibling tools like set_knob and clear_expression.

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?

Provides common expression examples and security restrictions, which imply usage context, but does not explicitly say when to use this tool versus set_knob or clear_expression. No exclusions or alternative routing are given.

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