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fetch-mcp

by YawLabs
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TypeScript
Remote

http_head

Read-onlyIdempotent

Check if a resource exists and inspect its HTTP status and headers without downloading the body. Use Content-Length to get file size or poll for changes with minimal bandwidth.

Instructions

Perform an HTTP HEAD. Returns status + headers with no body. Useful for checking a resource exists, getting its size (Content-Length), or polling for changes cheaply.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesTarget URL (http:// or https://)
headersNoExtra request headers as a key/value object
retriesNoRetries on 408/425/429/500/502/503/504 with exponential backoff (default 0)
max_bytesNoMax response body size in bytes before the body is truncated (default 5MiB, ceiling 100MiB)
basic_authNoHTTP Basic auth credentials
timeout_msNoRequest timeout in ms (default 10000, max 120000)
user_agentNoUser-Agent override (default identifies as @yawlabs/fetch-mcp)
decode_textNoForce text decoding (true) or binary base64 (false). Defaults to auto — text for text/*, json, xml, etc; binary otherwise.
bearer_tokenNoBearer token sent as Authorization: Bearer <token>
max_redirectsNoMax redirect hops to follow (default 5)
allow_private_hostsNoAllow requests to loopback / private / link-local addresses. SSRF protection is on by default — only flip this when intentionally talking to localhost.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.6.1

TDQS

A4.2/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior. The description adds the key behavioral detail that it returns status and headers with no body, going beyond the annotations, and notes the operation is 'cheap,' reinforcing its read-only nature. No contradiction with annotations.

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, front-loaded with the core action and outcome, followed by the main use cases. Every word is purposeful; there is no fluff or repetition.

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?

For a network tool with 11 parameters, the description covers the essential outcome and typical use cases. The schema fully documents parameters, and annotations cover safety, so nothing critical is missing. It could mention SSRF protection, but the schema already covers that.

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 the schema already documents all 11 parameters individually. The description adds no parameter-specific guidance beyond that, meeting the baseline of 3 without exceeding it.

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 description states a specific verb ('Perform an HTTP HEAD') with a clear resource and outcome (status + headers, no body). It lists concrete use cases (checking existence, Content-Length, cheap polling) that distinguish it from siblings like http_get which return a body.

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?

Provides explicit use cases: checking existence, getting Content-Length, and polling for changes. It implies preferring this over http_get when the body is not needed, but it does not explicitly name alternative tools or state when not to use it. The context is clear enough for an agent to select it appropriately.

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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