Retrieve a specific byte range from a URL to handle large files in manageable chunks, enabling partial downloads and targeted data access.
Fetch a byte range from a URL (chunked HTTP fetch)
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | HTTP/HTTPS URL to fetch | |
| start | No | Start byte offset (default 0) | |
| length | No | Number of bytes to fetch (default 65536) | |
| headers | No | Optional request headers |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations at all, the description carries the full burden of behavioral disclosure. It tells the agent that a range is fetched, but says nothing about HTTP method, response format, error behavior, redirects, or authentication. This is a thin behavioral picture for a network-fetching tool.
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 sentence with no filler. The core verb and object are front-loaded, and the parenthetical adds relevant clarity. Every word earns its place.
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 straightforward fetch tool with fully documented parameters, the description is minimally adequate. However, without an output schema or annotation safety profile, an agent does not know what the response looks like or how failures are surfaced, leaving a notable gap.
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 parameters url, start, length, and headers are already documented. The description's mention of 'byte range' loosely maps to start and length, but adds no detail beyond the schema 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?
The description states a clear verb ('Fetch') and resource ('a byte range from a URL'), and the parenthetical 'chunked HTTP fetch' reinforces the operation. It does not explicitly differentiate from sibling tools, but the purpose is specific and unambiguous.
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?
Usage is implied by the description: call this when you need a specific byte range of a URL rather than the full content. However, there is no explicit guidance on when not to use it or reference to alternatives among the siblings, so the guidance remains implicit.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.