Set a kerning pair value between two glyphs.
AI agents use set_kerning_pair 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 modifies font kerning data but the changes are reversible—kerning values can be adjusted again or reset. It does not delete data (Destructive), execute arbitrary code (Execute), or involve financial transactions (Financial). The 'medium' severity reflects that misuse could degrade font quality and require rework, but changes remain undoable and are localized to a single design artifact.
From the tool's definition Tool name 'set_kerning_pair' indicates a modification operation. Description explicitly states 'Set a kerning pair value between two glyphs,' which creates or modifies font metadata (kerning data) reversibly within the font design.
Documented attack patterns abuse exactly the kind of access set_kerning_pair 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_kerning_pair:
{
"version": "1",
"default": "deny",
"tools": {
"set_kerning_pair": {
"limits": [
{
"counter": "set_kerning_pair_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_kerning_pair 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 a kerning pair value between two glyphs. 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_kerning_pair: 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_kerning_pair 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_kerning_pair 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_kerning_pair. 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_kerning_pair 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.