browser-firefox-mcp

by ironessi

Overview Schema Source Related Servers Discussions Admin

Python

Local

set_cookie

Set a cookie value in the browser to manage session state during security testing and penetration workflows.

Instructions

Set a single cookie. Useful for session token replay.

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": {
      "name": "<name>",
      "value": "<value>"
    },
    "name": "set_cookie"
  }
}

Input Schema

Name	Required	Default
`name`	Yes
`path`	No	/
`value`	Yes
`domain`	No	.localhost
`secure`	No
`http_only`	No
`same_site`	No	Lax

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 20, 2026

TDQS

B3.1/5.0

Behavior2/5

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

With no annotations provided, the description carries the full burden of disclosing behavior. It only states the basic action 'Set a single cookie' and does not mention side effects such as whether it overwrites existing cookies, requires a loaded page, or any security considerations. For a mutation tool, this is insufficient disclosure.

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

Conciseness4/5

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

The description is a single, short sentence with no redundant words. It is appropriately concise, though it sacrifices informative content for brevity. Given the tool's complexity, it could benefit from a bit more detail without becoming verbose, so a 4 is appropriate.

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

Completeness1/5

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

This tool has 7 parameters, no annotations, and no output schema. The description provides only a minimal statement of purpose and a vague use case, leaving the agent without essential information about parameter semantics, behavioral implications, or when to use it. It is severely under-specified for a tool of this complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters1/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, and the description provides no information about any of the 7 parameters. It merely mentions the action but does not explain the meaning of name, value, path, domain, secure, http_only, or same_site. The description adds no value beyond the schema's field names, making it entirely unhelpful for parameter understanding.

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 clearly states the tool's function: 'Set a single cookie' with the verb 'Set' and resource 'cookie', and it specifically notes the difference from sibling set_cookies by indicating 'single'. The added context 'Useful for session token replay' gives a concrete use case, making the purpose unambiguous.

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 description provides a clear use case ('session token replay') and implicitly differentiates from set_cookies (plural) by indicating this is for a single cookie. However, it does not explicitly state when not to use it or mention alternatives, so it falls short of full guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.