This record as markdown: /tools/io-tinyfn-tinyfn/build-url.md
What build_url does on TinyFn
AI agents use build_url to create or update resources in TinyFn, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your TinyFn environment.
| Parameter | Type | Required | Description |
|---|---|---|---|
base | string | Yes | Base URL |
path | string | — | Path to append |
params | string | — | Query params as key=value&key2=value2 |
Parameters from the server's own tool schema.
Why build_url is rated Medium
This tool constructs/assembles a URL string from its parts (scheme, host, path, query, etc.). It creates/writes a new data structure (a URL string) but has no side effects on external systems—it's a pure string-building operation. Write is the closest category since it 'creates' output, though it's essentially a deterministic transformation. No execution, deletion, or financial impact possible.
From the tool's definition Build a URL from components
Risk signalsAccepts file system path (path)
Attacks that exploit this kind of access
The rule that runs build_url safely
PolicyLayer is an MCP gateway: it sits between your AI agents and TinyFn, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For build_url, this is the rule to start with:
build_url 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.
The button opens the PolicyLayer dashboard: create your workspace, connect TinyFn, apply this rule, and every build_url call is checked against it from then on.
Questions about build_url
Build a URL from components. It is categorised as a Write tool in the TinyFn MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
build_url accepts 3 parameters: base, path, params. Required: base. The full parameter table on this page comes from the server's own tool schema.
Register the TinyFn MCP server in PolicyLayer and add a rule for build_url: 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 TinyFn. Nothing to install.
build_url is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the build_url 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.
Set action: deny in the PolicyLayer policy for build_url. 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.
build_url is provided by the TinyFn MCP server (https://api.tinyfn.io/mcp/all/). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
More on TinyFn, and thousands of servers like it.
This server
Across the catalogue