AI agents use create_glyph 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.
Creating a glyph adds new font design data to the document, which is a reversible write operation (the glyph can be deleted or modified later). This is not destructive (not irreversible), not execute (not running arbitrary code), and not financial. The medium severity reflects that misuse could corrupt a font project, but the impact is scoped to a single design document and reversible.
From the tool's definition Tool name 'create_glyph' combined with server description indicating bidirectional read/write capability in GlyphsApp font editor. The server explicitly states it 'write[s] font data directly in GlyphsApp.'
Documented attack patterns abuse exactly the kind of access create_glyph 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 create_glyph:
{
"version": "1",
"default": "deny",
"tools": {
"create_glyph": {
"limits": [
{
"counter": "create_glyph_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create_glyph 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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create_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 create_glyph: 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.
create_glyph 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 create_glyph 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 create_glyph. 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.
create_glyph 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.