list_backends

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

With no annotations provided, the description must carry the behavioral burden. It discloses the output format ('a list of {name, available, module} entries') and implies it is a read-only diagnostic operation (no side effects are mentioned). This is sufficient for a simple listing tool, though it does not describe edge cases or error handling, which are minor for this type of function.

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 two sentences, front-loading the purpose and return structure first, then adding a practical usage example. Every word earns its place; there is no filler or redundancy. It is concise yet informative.

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 zero-parameter tool with an output schema (flag true), the description provides all needed context: it explains what the tool returns, why it exists (debugging backend availability), and how it relates to the router fallback scenario. The agent can correctly invoke and interpret the result without additional documentation.

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 tool has zero parameters, so the baseline is 4. The schema (empty object) already fully documents that no arguments are needed. The description reinforces that by focusing entirely on output and usage, adding no unnecessary parameter details. This 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 clearly states what the tool does: reports which parse backends are installed and which are missing. It specifies the resource ('parse backends') and the action ('Report') and differentiates it from sibling tools like parse or parse_url, which actually perform parsing rather than inspecting backend availability. The return shape is also given, making the purpose unambiguous.

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 description gives a concrete use case: 'Use this to debug "why did the router fall back to markitdown" by checking whether docling/llamaparse are actually available.' This tells the agent when this tool is appropriate (diagnosing fallback behavior) and implicitly distinguishes it from parsing tools. It does not explicitly mention when *not* to use it or name alternatives, but the context is clear enough for a zero-parameter utility.

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