cast-spell
Execute a NIP-A7 Spell (kind 777). Fetches the Spell event, resolves runtime variables ($me → your pubkey, $contacts → your follow list) and relative timestamps (e.g.
This record as markdown: /tools/dev-forgesworn-bray/cast-spell.md
What cast-spell does on Nostr Bray
AI agents invoke cast-spell to trigger actions in Nostr Bray. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
Why cast-spell is rated High
This tool executes arbitrary spells (NIP-A7 events) with runtime variable resolution. While the exact payload of a spell is not specified in the description, the core function—fetching an event and executing it with variable substitution—constitutes code execution. The effects are dependent on the spell's contents and could range from read operations to destructive actions in the Nostr ecosystem.
From the tool's definition Tool name 'cast-spell' combined with description stating it 'Execute[s] a NIP-A7 Spell (kind 777)' and 'resolves runtime variables' indicates runtime code execution.
Attacks that exploit this kind of access
The rule that runs cast-spell safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Nostr Bray, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For cast-spell, this is the rule to start with:
cast-spell stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Nostr Bray, apply this rule, and every cast-spell call is checked against it from then on.
Questions about cast-spell
Execute a NIP-A7 Spell (kind 777). Fetches the Spell event, resolves runtime variables ($me → your pubkey, $contacts → your follow list) and relative timestamps (e.g. It is categorised as a Execute tool in the Nostr Bray MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Nostr Bray MCP server in PolicyLayer and add a rule for cast-spell: 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 Nostr Bray. Nothing to install.
cast-spell is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the cast-spell 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 cast-spell. 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.
cast-spell is provided by the Nostr Bray MCP server (nostr-bray). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
More on Nostr Bray, and thousands of servers like it.
Across the catalogue