AI agents use add_signature_field to create or update resources in PDF Tools — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your PDF Tools environment.
This tool creates or adds new signature fields to PDFs, which is a reversible modification of document structure. It does not delete data (not Destructive), does not execute arbitrary code (not Execute), does not involve payments (not Financial), and does not just read data (not Read).
From the tool's definition Tool name 'add_signature_field' and description 'Draw a visible' indicates adding/creating new signature field elements to a PDF document, which modifies the PDF structure.
Documented attack patterns abuse exactly the kind of access add_signature_field gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and PDF Tools, and nothing reaches the server without passing your rules. This is the rule we recommend for add_signature_field:
{
"version": "1",
"default": "deny",
"tools": {
"add_signature_field": {
"limits": [
{
"counter": "add_signature_field_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_signature_field 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.
Free to start. No card required.
Draw a visible. It is categorised as a Write tool in the PDF Tools MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the PDF Tools MCP server in PolicyLayer and add a rule for add_signature_field: 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 PDF Tools. Nothing to install.
add_signature_field 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 add_signature_field 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 add_signature_field. 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.
add_signature_field is provided by the PDF Tools MCP server (open-document-alliance/pdf-tools). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 36 PDF Tools tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
36 PDF Tools tools catalogued and risk-classified — across an index of 42,500+ MCP servers.