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fetch-mcp

by YawLabs
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TypeScript
Remote

http_put

DestructiveIdempotent

Perform an HTTP PUT to replace a full resource on a web server. Configure headers, body, auth, retries, and timeouts for idempotent resource updates.

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_msNoTimeout in ms for each attempt, covering DNS, every redirect hop and the body (default 10000, max 120000). Retries get a fresh budget; a whole call is capped at 5 minutes.
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 loopback / private / link-local targets for this call (default false). Refused unless the server operator launched fetch-mcp with FETCH_MCP_ALLOW_PRIVATE_HOSTS=1 -- SSRF protection stays on by default either way.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.8.0
    • changedInput schema / properties / allow_private_hosts / description
      Previous value: -"Allow requests to loopback / private / link-local addresses. SSRF protection is on by default — only flip this when intentionally talking to localhost."New value: +"Allow loopback / private / link-local targets for this call (default false). Refused unless the server operator launched fetch-mcp with FETCH_MCP_ALLOW_PRIVATE_HOSTS=1 -- SSRF protection stays on by default either way."
    • changedInput schema / properties / timeout_ms / description
      Previous value: -"Request timeout in ms (default 10000, max 120000)"New value: +"Timeout in ms for each attempt, covering DNS, every redirect hop and the body (default 10000, max 120000). Retries get a fresh budget; a whole call is capped at 5 minutes."
  2. First observedv0.6.1

TDQS

A3.9/5.0
Behavior3/5

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

Annotations already declare idempotentHint=true, destructiveHint=true, and readOnlyHint=false. The description restates idempotency ('the same PUT applied twice leaves the resource in the same state') and adds 'full-resource replacement' as semantic context, but does not disclose additional behaviors like error handling or response format. 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?

Two concise sentences with no filler. The core action is front-loaded ('Perform an HTTP PUT'), followed by the key semantic reason to use it and a clarifying idempotency note.

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?

The schema is rich and annotations cover safety and idempotency, making the tool callable correctly. However, there is no output schema and the description does not explain what the tool returns (e.g., response status, headers, body) or edge cases like SSRF blocking, leaving some contextual ambiguity.

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%, with thorough parameter descriptions including defaults, retries, SSRF protection, and timeout behavior. The description itself adds no parameter-level information, so the baseline score of 3 applies.

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?

States a specific verb and resource ('Perform an HTTP PUT') plus its semantic role ('full-resource replacement'), which clearly distinguishes it from siblings like http_patch (partial update) and http_post (create/submit). The description is unambiguous about what the tool does.

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 a clear usage context: 'Use for full-resource replacement.' This tells the agent when to prefer this tool over sibling methods, though it does not explicitly name alternatives or state when not to use it.

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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