I bond rate MCP server (free, no API key)

Looking for an MCP server for the current I bond rate? i-bond-rate-mcp is free, MIT licensed and needs no API key and no account. Paste https://i-bond-rate-mcp.lipmichal.workers.dev/mcp into any MCP client that takes a remote server URL. Current I bond rate, what your I bond earns by issue month, and value estimates from TreasuryDirect.

Tools 5, version 1.0.0, licence MIT. Part of the free live-data MCP servers on this hub.

What it answers that a model cannot answer alone

A language model answers from training data that is months old and does arithmetic from memory. This server returns the current figure with its source. In the words of its README, it knows these things that your model does not.

  1. The November 2026 rates (5.51 percent composite, 1.40 percent fixed, 2.04 percent semiannual inflation). Treasury announced them on November 1, 2026.
  2. That an existing bond does not earn the new-bond rate. It keeps its own fixed rate and gets a new inflation rate every 6 months from its issue month, so a bond bought in April 2022 earns 3.34 percent from October 2026 while a bond bought in January 2023 earns 3.75 percent until January 2027.
  3. The exact rounding and the zero floor. The formula reproduces all 1,711 composite rates in the Treasury chart.

Connect it with no key

Hosted URL for Claude.ai custom connectors, ChatGPT developer mode and any client that takes a remote MCP server. Paste it as is. No token, no sign-up.

https://i-bond-rate-mcp.lipmichal.workers.dev/mcp

Claude Code, hosted or local:

claude mcp add --transport http i-bond-rate https://i-bond-rate-mcp.lipmichal.workers.dev/mcp
claude mcp add i-bond-rate -- npx -y github:theluckystrike/i-bond-rate-mcp

Claude Desktop (claude_desktop_config.json), runs locally with Node 20 or newer:

{
  "mcpServers": {
    "i-bond-rate": { "command": "npx", "args": ["-y", "github:theluckystrike/i-bond-rate-mcp"] }
  }
}

Cursor (~/.cursor/mcp.json):

{
  "mcpServers": {
    "i-bond-rate": { "url": "https://i-bond-rate-mcp.lipmichal.workers.dev/mcp" }
  }
}

Tools it exposes

Tool What it does
get_current_i_bond_rate Current Series I savings bond composite rate, fixed rate and semiannual inflation rate for new purchases, read at call time from the TreasuryDirect “I bonds interest…
get_i_bond_rate_for_issue_date For an I bond bought in a given month: its fixed rate, the composite rate it earns in the current (or given) 6-month period, the months its rate changes, whether it can…
estimate_i_bond_value Estimate what I bonds are worth for an issue month and purchase amount at the start of a month: value with all interest and the redemption value after the 3-month…
calculate_i_bond_composite_rate Apply the Treasury formula fixed + 2 x semiannual inflation + fixed x semiannual inflation, rounded to 0.01 percent with a floor of zero.
get_i_bond_rate_history Fixed rate for new bonds, semiannual inflation rate and composite rate for every May and November announcement since September 1998, newest first, from the…

Example output from a live call

Called on 2026-11-05 against the hosted URL above, with no token. The prompt was “What is the I bond rate for bonds bought in November 2026?” and the client sent this call.

{"name": "get_current_i_bond_rate", "arguments": {}}

The server answered with this plain-English summary (the structured JSON that follows it in the result is left out here).

I bonds bought from November 2026 through April 2027 earn 5.51% a year for their first 6 months: a 1.40% fixed rate that lasts for the life of the bond plus 2.04% semiannual inflation rate. Treasury sets the next rates on May 1, 2027. Limit $10,000 in electronic I bonds per Social Security number per calendar year, $25 minimum, held at least 12 months, last 3 months of interest lost if cashed before 5 years.

Data as of 2026-11-05T14:15:34.347Z. The result also returns the source URL and a link for more detail.

Questions people actually ask

Is there an MCP server for the current I bond rate?

Yes. I bond rate (i-bond-rate-mcp) is a free MCP server. Current I bond rate, what your I bond earns by issue month, and value estimates from TreasuryDirect. It is hosted at https://i-bond-rate-mcp.lipmichal.workers.dev/mcp with no token, and it also runs locally with npx -y github:theluckystrike/i-bond-rate-mcp.

Does the I bond rate MCP server need an API key?

No. The hosted endpoint answers tools/list and tools/call without a token or sign-up. The example on this page was called that way on 2026-11-05.

Is it free?

Yes. The code is MIT licensed and the hosted endpoint is free to call. This server has no paid tier at all.

Where do the numbers come from?

Each result carries an as_of date and a source. In the live call on this page the source was https://www.treasurydirect.gov/savings-bonds/i-bonds/i-bonds-interest-rates/. The full source list is in DATA_SOURCES.md in the repository.

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