OpenRouter MCP Server

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

No annotations are provided, so the description carries full burden for behavioral disclosure. It mentions filtering and sorting capabilities but doesn't describe important behavioral aspects like whether this is a read-only operation, how results are paginated, what authentication is required, rate limits, or what the output format looks like. The description provides basic functionality but lacks critical operational context.

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 perfectly structured and concise. It starts with the core purpose, then provides parameter documentation in a clear 'Args:' section. Every sentence earns its place by either stating the tool's function or explaining parameter usage. No wasted words or redundant information.

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?

Given that there's an output schema (which handles return values), 2 parameters with good documentation in the description, and no complex behavioral requirements, the description is reasonably complete. It covers the tool's purpose and parameter semantics well. The main gap is the lack of behavioral context (like pagination or authentication), but the output schema reduces the need to describe return values.

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 description adds significant value beyond the input schema, which has 0% description coverage. It provides the semantics for both parameters: 'modality' with options 'text, image, audio, embeddings, all' and 'sort_by' with options 'name, created, price, context_length'. This completely documents what would otherwise be undocumented parameters, making it easy for an agent to understand how to use them correctly.

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 the tool's purpose: 'List models available on OpenRouter.' This specifies the verb ('List') and resource ('models available on OpenRouter'), making it easy to understand what the tool does. However, it doesn't explicitly differentiate from sibling tools like 'search_models' or 'compare_models', which prevents a perfect score.

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 provides no guidance on when to use this tool versus alternatives. With sibling tools like 'search_models', 'compare_models', and 'get_model', there's no indication of when this list operation is preferred over more specific queries. The description only documents parameters without contextual usage advice.

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