Read an S3 object's contents inline as text or base64, up to 262144 bytes. For larger objects, use a presigned URL instead.
Read at most 262144 bytes inline as text/base64; use presign for larger objects.
| 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 and does disclose two meaningful traits: a hard 262144-byte truncation cap and that content is returned as text or base64. It omits permission requirements, error behavior for missing keys, and whether truncated output is flagged, leaving real gaps for a read tool with zero annotation coverage.
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 dense sentence with the size constraint and output format front-loaded, followed immediately by the routing alternative. No filler; every clause carries 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?
For a read tool with no annotations and no output schema, the description covers the essential size/encoding behavior but leaves key gaps: version_id handling, truncation signaling, and failure modes. Adequate to call the tool, not complete for an agent to do so confidently.
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 coverage is 0% with 5 parameters, so the description must compensate. It partially does: the byte cap implies max_bytes and 'text/base64' implies encoding, but version_id is never mentioned and its semantics are undocumented in both schema and description.
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 and resource (read an S3 object) plus a concrete scope for the operation (at most 262144 bytes, inline as text/base64). It explicitly distinguishes itself from s3_presign_get, but says nothing about how it differs from near-neighbors like s3_head_object or s3_preview_object, so the differentiation is partial.
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?
Gives an explicit when-not condition ('use presign for larger objects') and names the alternative tool, which is exactly the routing decision an agent needs. It stops short of a full when/when-not picture because it never addresses metadata-only (s3_head_object) or preview (s3_preview_object) use cases.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.