llen

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

The description implies a non-destructive read operation, but lacks explicit statements about side effects, error handling (e.g., if key does not exist), or permissions. Without annotations, some behavioral responsibility remains undeclared.

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?

A single, clear sentence. It is concise and front-loaded, but could be expanded slightly to include parameter context without losing brevity.

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 tool with an output schema, the description is adequate but incomplete; it does not mention return value type (integer) or behavior when key is missing, which are important for agent understanding.

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?

The parameter 'name' has no description in the schema (0% coverage), and the tool description does not clarify that it represents the Redis key of the list. The parameter's purpose is inferable but not explicitly documented.

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 'Get the length of a Redis list.' clearly states the action (get length) and resource (Redis list), effectively distinguishing it from sibling commands like lpush, lpop, lrange, etc.

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?

No guidance on when to use this tool versus alternatives (e.g., llen vs. lrange for checking list size). The description provides no context for optimal usage or prerequisites.

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