Databento MCP

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

With no annotations provided, the description carries full burden for behavioral disclosure. It mentions 'Subscribe' (implying a streaming/ongoing operation) and 'limited duration', but fails to describe critical behaviors: whether this is read-only or has side effects, authentication requirements, rate limits, error handling, or what happens when the stream ends. For a real-time data tool, this leaves significant gaps.

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 a single, efficient sentence that gets straight to the point with zero wasted words. It's appropriately sized for the tool's complexity and front-loads the core purpose without unnecessary elaboration.

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 real-time data subscription tool with no annotations and no output schema, the description is insufficient. It doesn't explain what format the data arrives in, whether it's a stream or batch return, how errors are handled, or what permissions are required. The combination of missing behavioral context and no output information creates significant gaps for an agent trying to use this tool effectively.

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 schema already documents all parameters thoroughly. The description doesn't add any meaningful parameter semantics beyond what's in the schema - it doesn't explain relationships between parameters, provide examples beyond what's implied, or clarify edge cases. Baseline 3 is appropriate when schema does the heavy lifting.

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 action ('Subscribe to real-time market data') and resource ('market data'), making the purpose understandable. However, it doesn't specifically differentiate from sibling tools like 'get_historical_data' beyond the 'real-time' qualifier, which is implied but not explicit.

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 mentions 'for a limited duration' which provides some context about temporal constraints, but it doesn't explicitly state when to use this tool versus alternatives like 'get_historical_data' or 'get_dataset_range'. No guidance on prerequisites, error conditions, or specific use cases is provided.

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