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fetch-mcp

by YawLabs
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TypeScript
Remote

http_put

DestructiveIdempotent

Replace a web resource entirely by sending an HTTP PUT request to a target URL. Idempotent, so repeated calls leave the resource unchanged after the first successful update.

Instructions

Perform an HTTP PUT. Use for full-resource replacement. Idempotent: the same PUT applied twice leaves the resource in the same state.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesTarget URL (http:// or https://)
bodyNoRaw request body as a string
headersNoExtra request headers as a key/value object
retriesNoRetries on 408/425/429/500/502/503/504 with exponential backoff (default 0)
body_jsonNoRequest body as a JSON value — sets content-type to application/json if none given
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>
content_typeNoContent-Type header to send with the body (e.g. application/json, text/plain, application/x-www-form-urlencoded)
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 indicate idempotentHint=true, destructiveHint=true, and readOnlyHint=false. The description adds value by explaining idempotence in plain terms ('the same PUT applied twice leaves the resource in the same state') and clarifying the replacement semantics. It does not contradict the 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?

The description is two tight sentences with no filler. The purpose is front-loaded, and the idempotency clarification is useful, not redundant.

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 generic HTTP client with 14 parameters and no output schema, the description covers the essential selection criteria: that it is a full-resource replacement and idempotent. The rich parameter schema and annotations carry the remaining burden, though response format and explicit exclusions are left implicit.

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?

All 14 parameters are already documented in the input schema with individual descriptions, giving 100% schema description coverage. The tool description adds no parameter-level information, so the baseline score of 3 is appropriate.

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 'Perform an HTTP PUT' and adds 'Use for full-resource replacement', which gives a specific semantic meaning beyond the tool name. This also clearly distinguishes it from siblings like http_patch, which would handle partial updates.

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 phrase 'Use for full-resource replacement' provides a clear, explicit condition for when to invoke this tool. It does not explicitly name alternatives or say 'do not use for partial updates', so it falls just short of full when/when-not guidance.

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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