mcp-server-s3

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions optional filtering but fails to describe key behaviors: whether this is a read-only operation (implied but not stated), how results are returned (e.g., pagination, format), error conditions, or rate limits. For a tool with 3 parameters and no annotation coverage, 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 front-loads the core purpose ('List objects in an S3 bucket') and adds optional details concisely. Every word earns its place, with no redundancy or unnecessary elaboration, making it easy to parse quickly.

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 the tool's moderate complexity (3 parameters, no output schema, no annotations), the description is adequate but incomplete. It covers the basic purpose and optional parameters but lacks details on behavior, output format, or error handling. This makes it minimally viable but with clear gaps for effective agent use.

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 fully documents all parameters (bucket, prefix, maxKeys). The description adds marginal value by mentioning 'prefix' and 'limit count' (referring to maxKeys), but doesn't provide additional semantics beyond what's in the schema, such as examples or constraints. Baseline 3 is appropriate when the 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 verb ('List') and resource ('objects in an S3 bucket'), making the purpose immediately understandable. It distinguishes this from siblings like 'list_buckets' (which lists buckets rather than objects) and 'get_object' (which retrieves a specific object). However, it doesn't explicitly mention that this lists ALL objects matching criteria, which would make it a perfect 5.

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 implies usage through the optional filtering parameters ('Optionally filter by prefix and limit count'), suggesting when to use these features. However, it lacks explicit guidance on when to choose this tool over alternatives like 'list_buckets' (for buckets) or 'get_object' (for specific objects), and doesn't mention prerequisites or exclusions.

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