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s3_list_objects

List objects and folders in an S3 bucket with optional prefix filtering. Returns keys, sizes, and truncation status to navigate large buckets.

Instructions

List objects and virtual-folder prefixes in an S3 bucket. Returns a JSON object with 'folders', 'objects' (each with key/size/last_modified), and 'is_truncated' (true when the bucket has more than ~1000 keys matching the prefix — re-call with a more specific prefix).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
bucketYesBucket name.
prefixNoKey prefix to filter by (default: '').
regionNoRegion the bucket lives in (e.g. 'eu-central-1'). Omit unless you know it — it is resolved automatically. AWS, and OVH when no endpoint URL is configured (pass the region s3_list_buckets reports). Rejected for Hetzner, and for an OVH endpoint URL set by hand, whose region is fixed by that endpoint.
accountNoAccount label of the provider whose object storage to use; omit for that provider's default account.
providerYesStorage provider.
delimiterNoDelimiter for virtual folder grouping (default: '/')./

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv2.28.0
    • addedInput schema / properties / account
      Added value: +{
+  "description": "Account label of the provider whose object storage to use; omit for that provider's default account.",
+  "type": "string"
+}
    • changedInput schema / properties / region / description
      Previous value: -"Region the bucket lives in (e.g. 'eu-central-1'). Omit unless you know it — it is resolved automatically. AWS only; rejected for Hetzner/OVH, whose region is fixed by the configured endpoint URL."New value: +"Region the bucket lives in (e.g. 'eu-central-1'). Omit unless you know it — it is resolved automatically. AWS, and OVH when no endpoint URL is configured (pass the region s3_list_buckets reports). Rejected for Hetzner, and for an OVH endpoint URL set by hand, whose region is fixed by that endpoint."
  2. Changed1 schema field changedv2.24.2
    • addedInput schema / properties / region
      Added value: +{
+  "description": "Region the bucket lives in (e.g. 'eu-central-1'). Omit unless you know it — it is resolved automatically. AWS only; rejected for Hetzner/OVH, whose region is fixed by the configured endpoint URL.",
+  "type": "string"
+}
  3. Addedv2.24.0
  4. Removedv2.23.8
  5. First observedv1.0.0

TDQS

A4.2/5.0
Behavior4/5

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

With no annotations, the description carries the full burden and does well: it discloses the return fields, the ~1000 key cap, and the truncation-recovery procedure. It stops short of permission/auth requirements or provider-specific behavior for the region/account parameters.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, both earning their place: the first defines the operation, the second defines the output and the pagination escape hatch. The output contract is front-loaded and there is no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema and no annotations, so the description must explain returns — and it does, naming folders/objects/is_truncated and the key fields. For a 6-parameter read tool this is nearly complete; only provider/account/region semantics are left entirely to the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and every parameter is documented in the schema, so the baseline is 3. The description only alludes to 'prefix' (via 'more specific prefix') and 'delimiter' (via 'virtual-folder prefixes'), adding no format or syntax details beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The first sentence states a specific verb ('List') and resource ('objects and virtual-folder prefixes in an S3 bucket'), and the second sentence pins down the exact return shape. An agent can distinguish this from s3_list_buckets purely from the description, since this tool operates inside a single bucket.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives actionable guidance for the truncated case: re-call with a more specific prefix when 'is_truncated' is true. It does not, however, contrast itself with alternatives like s3_list_buckets, nor state prerequisites (e.g. that bucket/provider are required) beyond what the schema already says.

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

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