validateJWTWithId
Validates the provided JWT (encoded JWT string) to ensure the token is valid. A valid access token is properly signed and not expired. <p> This API may be used to verify the JWT as well as decode the encoded JWT into human readable identity claims.
This record as markdown: /tools/io-fusionauth-mcp-api/validatejwtwithid.md
What validateJWTWithId does on Fusionauth
AI agents call validateJWTWithId to retrieve information from Fusionauth without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why validateJWTWithId is rated Low
validateJWTWithId performs cryptographic validation and decoding of JWT tokens to inspect claims and verify signatures. This is a pure read operation with no side effects—it does not create, modify, delete, or execute external operations. The tool retrieves and validates information from an encoded token without altering state.
From the tool's definition Tool name and description explicitly state it 'Validates' and 'decode[s]' a JWT token—no modification, deletion, or execution of arbitrary code. The description emphasizes verification and decoding of claims, which are read-only operations.
Attacks that exploit this kind of access
The rule that runs validateJWTWithId safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Fusionauth, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For validateJWTWithId, this is the rule to start with:
validateJWTWithId is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Fusionauth, apply this rule, and every validateJWTWithId call is checked against it from then on.
Questions about validateJWTWithId
Validates the provided JWT (encoded JWT string) to ensure the token is valid. A valid access token is properly signed and not expired. <p> This API may be used to verify the JWT as well as decode the encoded JWT into human readable identity claims. It is categorised as a Read tool in the Fusionauth MCP Server, which means it retrieves data without modifying state.
Register the Fusionauth MCP server in PolicyLayer and add a rule for validateJWTWithId: 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 Fusionauth. Nothing to install.
validateJWTWithId is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the validateJWTWithId 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 validateJWTWithId. 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.
validateJWTWithId is provided by the Fusionauth MCP server (@fusionauth/mcp-api). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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