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Fulcra MCP Server

Fulcra MCP Server

by fulcradynamics
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Upload File Chunk

upload_file_chunk

Uploads one base64-encoded file chunk at a specified byte offset for an active upload session, enabling large files to be sent in parts.

Instructions

Sends one chunk of an upload from the file manager panel.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "upload_id": "<upload_id>",
      "offset": "<offset>",
      "data": "<data>"
    },
    "name": "upload_file_chunk"
  }
}

Input Schema

NameRequiredDescriptionDefault
dataYesThe chunk, base64.
offsetYesChunk start, in bytes.
upload_idYesFrom start_file_upload.

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv1.18.7
    • changedInput schema / properties / data / description
      Previous value: -"The chunk, base64-encoded. Every chunk but the last must be a\nmultiple of 256 KiB, and at most 8 MiB."New value: +"The chunk, base64."
    • changedInput schema / properties / offset / description
      Previous value: -"Where this chunk starts in the file, in bytes; chunks go in\norder. Resending a chunk that already arrived is harmless."New value: +"Chunk start, in bytes."
  2. Addedv1.2.4

TDQS

C2.6/5.0
Behavior2/5

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

Annotations already state readOnlyHint=false and destructiveHint=false, so safety is covered. The description adds little beyond 'from the file manager panel', which is irrelevant to an agent, and omits ordering, idempotency/retry, whether re-sending an offset overwrites data, and any size constraints.

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

Conciseness3/5

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

A single short sentence with no padding, so it is concise, but the length comes at the cost of under-specification rather than efficiency. The useful part (chunk of an upload) is front-loaded.

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

Completeness3/5

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

An output schema exists and the input schema is fully documented, so the basics are covered. However, a chunked-upload step tool is incomplete without sequencing and finalization guidance, which the description entirely omits.

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%, so each of upload_id, offset, and data is already documented in the schema. The description adds no extra meaning to any of the three parameters, which is the expected baseline when the schema does the work.

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

Purpose3/5

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

The verb+resource combo ('Sends one chunk of an upload') is specific about the action, but it never explains the chunked-upload protocol it belongs to or how it relates to start_file_upload. An agent knows it moves bytes but not the larger workflow it participates in.

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

Usage Guidelines2/5

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

There is no when-to-use guidance at all: not when to start chunking, how many times to call, whether chunks must be sequential, or what to call to finalize the upload. The only hint is the schema's note that upload_id comes from start_file_upload.

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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