set_context · Fastly NGWAF MCP Server MCP: Risk & Policy

WHAT IT DOES

What set_context does on Fastly NGWAF MCP Server

AI agents use set_context to create or update resources in Fastly NGWAF MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fastly NGWAF MCP Server environment.

WHY IT NEEDS A POLICY

Why set_context needs a policy

This tool writes/modifies configuration state by setting default context parameters. It is reversible (context can be changed again), so it does not qualify as Destructive. It does not execute external code or operations (Execute), nor does it retrieve data (Read).

From the tool's definition Tool description states 'Set the default corporation and site context for subsequent operations' - this modifies state (context settings) that affects how subsequent operations behave.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_context Rate-limited

set_context stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_context": {
      "limits": [
        {
          "counter": "set_context_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Fastly NGWAF MCP Server, so you can run agents against it safely.

FAQ

Questions about set_context

What does the set_context tool do? +

Set the default corporation and site context for subsequent operations. It is categorised as a Write tool in the Fastly NGWAF MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_context? +

Register the Fastly NGWAF MCP Server MCP server in PolicyLayer and add a rule for set_context: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Fastly NGWAF MCP Server. Nothing to install.

What risk level is set_context? +

set_context is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_context? +

Yes. Add a rate_limit block to the set_context rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block set_context completely? +

Set action: deny in the PolicyLayer policy for set_context. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides set_context? +

set_context is provided by the Fastly NGWAF MCP Server MCP server (purpleax/fastlymcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.