Preview the first bytes of an S3 object to inspect its detected content type and CSV header before downloading or processing the full file.
Preview first at most 65536 bytes, detected type and CSV header.
| Name | Required | Description | Default |
|---|---|---|---|
| key | Yes | ||
| bucket | Yes | ||
| encoding | No | ||
| max_bytes | No | ||
| version_id | No |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden. It discloses important traits such as the byte cap (65536) and partial-read behavior, and it mentions return content (detected type, CSV header). However, it omits read-only confirmation, permissions, side effects, error behavior, and rate/cost 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?
A single front-loaded sentence with no wasted words. It is appropriately sized for the description's scope, even though the content itself is sparse.
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 tool with five parameters, no output schema, and no annotations, the description is too sparse. It gives some return information but omits parameter semantics, access requirements, and operational constraints, leaving an agent under-informed for correct invocation.
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 0% and there are five parameters, yet the description explains none of them. It mentions '65536 bytes' and 'CSV header' but does not map these to max_bytes, encoding, bucket, key, or version_id, so it fails to compensate for the schema's lack of descriptions.
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?
States a specific verb ('preview') and resource ('object' via name), plus the scope ('first at most 65536 bytes') and return content ('detected type and CSV header'). It is clear enough to distinguish it from full-object retrieval, but it does not explicitly name or route against siblings like s3_get_object or s3_head_object.
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 is provided on when to use this tool versus s3_get_object, s3_head_object, or other siblings. The word 'preview' implies a use case, but there are no explicit conditions, exclusions, or alternatives stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.