Set the advance width of a glyph.
AI agents use set_glyph_width to create or update resources in Glyphs — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Glyphs environment.
This tool creates or modifies font glyph data (advance width) reversibly within GlyphsApp. While it changes font properties, the modification is not destructive (can be undone/reverted), nor does it execute arbitrary code or involve financial transactions.
From the tool's definition Tool name 'set_glyph_width' and description 'Set the advance width of a glyph' explicitly perform a write operation that modifies glyph metrics in the font data.
Documented attack patterns abuse exactly the kind of access set_glyph_width gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Glyphs, and nothing reaches the server without passing your rules. This is the rule we recommend for set_glyph_width:
{
"version": "1",
"default": "deny",
"tools": {
"set_glyph_width": {
"limits": [
{
"counter": "set_glyph_width_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_glyph_width 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.
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Set the advance width of a glyph. It is categorised as a Write tool in the Glyphs MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Glyphs MCP server in PolicyLayer and add a rule for set_glyph_width: 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 Glyphs. Nothing to install.
set_glyph_width 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 set_glyph_width 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 set_glyph_width. 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.
set_glyph_width is provided by the Glyphs MCP server (nmassi/glyphs-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Glyphs, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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41 Glyphs tools catalogued and risk-classified — across an index of 43,000+ MCP servers.