repl_set_variable

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

Annotations already mark the operation as idempotent and non-destructive. The description adds the return behavior ('Confirmation with variable type and preview') and emphasizes JSON parsing, which goes beyond the annotations without contradicting them.

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?

The description is concise and well-structured: a one-sentence purpose, a brief usage note, and a clear Returns section. No filler or redundant content.

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 simple three-parameter setter with idempotent and non-destructive annotations, the description plus schema adequately covers input, purpose, and return behavior. It could mention session existence prerequisites, but that is not essential for correct tool selection and invocation.

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?

Although the context signal reports 0% schema coverage, the actual input schema contains short descriptions for session_id, var_name, and json_value. The tool description reinforces that json_value must be a JSON string but does not add substantially new semantic meaning beyond the schema, so baseline 3 is appropriate.

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 opens with a specific action ('Set a variable in a session from a JSON string') that clearly identifies the tool's resource and input format. This distinguishes it from sibling tools like repl_get_variable and repl_delete_variable.

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?

The phrase 'Useful for injecting data from external sources' provides a clear use case. It does not explicitly list exclusions or alternatives, but the context is sufficient to guide tool selection.

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