send21
REMOTE · SEND21.IO · 2 COMPONENTS
Crypto pay links and API for people and AI agents. BTC, Lightning, USDC, USDT, EURC, SOL, ETH.
Available components
Last scanned (1 hour ago)
Scores higher than 99% of remote servers
Reachable. Last reached 5 Nov 2026.
Category Crypto and Web3
How this component scores in each security and reliability category. Every signal is checked automatically against the live server, and we only credit what we can confirm. How we score → Why this is hard to score →
Endpoint Security94
- The endpoint's TLS certificate is valid, in date, and uses a strong key. View diagnostics → Pass
- Authorisation is enforced on tool calls, advertised via RFC 9728 protected-resource metadata. Discovery is public, which costs nothing: no tool can be invoked without a token. View diagnostics → Pass
- HTTPS is enforced; there's no plaintext access path. View diagnostics → Pass
- The HSTS (Strict-Transport-Security) header is present. View diagnostics → Pass
- DNSSEC check failed: this domain isn't protected by DNSSEC. See how to fix → View diagnostics → Fail
- The authorisation server offers only Dynamic Client Registration (RFC 7591), which MCP 2026-07-28 deprecated in favour of Client ID Metadata Documents. View diagnostics → Partial
Transport & Reachability100
- Verified streamable-http transport via a live MCP handshake. View diagnostics → Pass
Schema Quality & AI Usability88
- 100% of prompts and resources have a non-trivial description (not blank, and not just the item's name).Pass
- AI-judged instruction clarity (excellent).Pass
- Tool/resource definitions use about 2580 tokens (~103/item across 25 items; 14 tools + 11 resources), lean.Pass
- Usage-examples check failed: none of the tools include examples. See how to fix → Fail
Stability & Change Management100
- No destabilizing schema changes in the last 30 days.Pass
Tool Coverage100
- 100% of tools have a non-trivial description (not blank, and not just the tool's name).Pass
- 100% of tool parameters carry a description.Pass
Tool Safety100
- No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.Pass
- We read all 14 captured tool definition(s), and no name or description among them implies an irreversible operation.Pass
- An AI judge read all 15 captured unit(s) of tool text and found none that tries to manipulate the model reading it.Pass
Capabilities100
- Implements a current MCP spec version (2026-07-28).Pass
Every change we have recorded for this component, newest first. Security-relevant changes are always shown. ▲ marks a change for the better, ▼ a change for the worse; unmarked changes are neutral.
- 22 Oct 26 +12
- Authorization: unverified → pass ▲ security
- First check of Authorization: partial security
- Server version: 1.5.0 → 1.7.0 functional
- Tool “create_account” changed its title: Create send21 account for owner cosmetic
- Tool “create_draft” changed its title: Create payment draft cosmetic
- Tool “create_payment_request” changed its title: Create pay link cosmetic
- Tool “get_account_status” changed its title: Get account status cosmetic
- Tool “get_draft” changed its title: Get payment draft cosmetic
- Tool “get_draft_status” changed its title: Get draft status cosmetic
- Tool “get_fee_schedule” changed its title: Get fee schedule cosmetic
- Tool “get_payment_request” changed its title: Get pay link cosmetic
- Tool “get_rate” changed its title: Get exchange rate cosmetic
- Tool “get_transaction_template” changed its title: Get wallet payment instructions cosmetic
- Tool “list_address_book” changed its title: List address book cosmetic
- Tool “list_draft_quotes” changed its title: List draft quotes cosmetic
- Tool “propose_receiving_address” changed its title: Propose receiving address cosmetic
- Tool “submit_lightning_proof” changed its title: Submit Lightning payment proof cosmetic
- 20 Oct 26 0
- Tool “create_draft” rewrote its description, which is the text the model reads security
- Tool “create_payment_request” rewrote its description, which is the text the model reads security
- Schema quality: 90 → 103 ▼ functional
- Server version: 1.4.0 → 1.5.0 functional
- New tool “create_account” functional
- New tool “get_account_status” functional
- New tool “propose_receiving_address” functional
- 19 Oct 26 +3
- The server changed its declared name: Send21.Api → send21 security
- Schema quality: fail → pass ▲ functional
- The server now declares the “prompts” capability functional
- The server now declares the “resources” capability functional
- First check of Schema quality: 100 functional
- New prompt “check_payment” functional
- New prompt “create_pay_link” functional
- New prompt “handle_amount_mismatch” functional
- New resource “brand-guidelines” functional
- New resource “currencies” functional
- New resource “fee-schedule” functional
- New resource “icon-on-dark” functional
- New resource “logo-horizontal-on-dark” functional
- New resource “logo-horizontal-on-dark-png” functional
- New resource “logo-stacked-on-dark” functional
- New resource “overview” functional
- New resource “webhook-guide” functional
- New resource “wordmark-on-dark” functional
- New resource “wordmark-on-light” functional
- Server version: 1.0.0.0 → 1.4.0 functional
- 13 Oct 26 −1
- “create_draft” reworded the description of “idempotencyKey” cosmetic
- “create_payment_request” reworded the description of “idempotencyKey” cosmetic
- “create_payment_request” reworded the description of “reuseOpenForOrder” cosmetic
- “create_draft” made “amountBaseUnits” optional cosmetic
- “create_draft” made “currency” optional cosmetic
- “create_draft” made “fiatAmount” optional cosmetic
- “create_draft” made “fiatCurrency” optional cosmetic
- “create_draft” made “idempotencyKey” optional cosmetic
- “create_draft” made “memo” optional cosmetic
- “create_payment_request” made “expiryHours” optional cosmetic
- “create_payment_request” made “idempotencyKey” optional cosmetic
- “create_payment_request” made “memo” optional cosmetic
- “create_payment_request” made “orderId” optional cosmetic
13 cosmetic changes on this day. Switch on “Show cosmetic changes” to see them.
- 12 Oct 26 0
- Tool “get_draft_status” rewrote its description, which is the text the model reads security
- Tool “get_payment_request” rewrote its description, which is the text the model reads security
- Schema quality: 118 → 144 ▼ functional
- Schema quality: 118 → 135 ▼ functional
- New tool “list_draft_quotes” functional
- “create_payment_request” added an optional parameter “reuseOpenForOrder” cosmetic
- “create_draft” added an optional parameter “shortfallAbsorbUpToPercent” cosmetic
- “create_payment_request” added an optional parameter “declineNote” cosmetic
- “create_payment_request” added an optional parameter “shortfallAbsorbUpToPercent” cosmetic
- 8 Oct 26 −1
- Tool “create_payment_request” rewrote its description, which is the text the model reads security
- Tool “get_rate” rewrote its description, which is the text the model reads security
- Tool “get_transaction_template” rewrote its description, which is the text the model reads security
- Schema quality: pass → fail ▼ functional
- New tool “submit_lightning_proof” functional
- 6 Oct 26 +1
- Stability: 0.93 → pass security
- 3 Oct 26 0
- Tool “create_draft” rewrote its description, which is the text the model reads security
- Tool “get_transaction_template” rewrote its description, which is the text the model reads security
- “create_draft” reworded the description of “idempotencyKey” cosmetic
- “create_payment_request” reworded the description of “idempotencyKey” cosmetic
- “create_payment_request” reworded the description of “orderId” cosmetic
Diagnostic detail from the automated scan of this channel: what the scanner observed at each step, so you can see exactly where a check passed or failed. It is informational only and never changes the trust score.
Captured 5 Nov 2026 · Probed https://send21.io/mcp
TLS valid
Negotiated TLS 1.3 with TLS_AES_128_GCM_SHA256 .
| Subject | Issuer | Valid from | Valid until | Key | Signature | Serial |
|---|---|---|---|---|---|---|
| CN=send21.io | CN=WE1,O=Google Trust Services,C=US | 7 Oct 2026 | 6 Jan 2027 | ECDSA 256 | ECDSA-SHA256 | 37fef1a2ef98a2bd13be76b4e961da37 |
| SANs: send21.io, *.send21.io | ||||||
| CN=WE1,O=Google Trust Services,C=US (CA) | CN=GTS Root R4,O=Google Trust Services LLC,C=US | 13 Dec 2023 | 20 Feb 2029 | ECDSA 256 | ECDSA-SHA384 | 7ff31977972c224a76155d13b6d685e3 |
| CN=GTS Root R4,O=Google Trust Services LLC,C=US (CA) | CN=GlobalSign Root CA,OU=Root CA,O=GlobalSign nv-sa,C=BE | 15 Nov 2023 | 28 Jan 2028 | ECDSA 384 | SHA256-RSA | 7fe530bf331343bedd821610493d8a1b |
Background: What to check on a remote MCP endpoint →
DNSSEC insecure
Validation of send21.io. — Not signed
| Zone | DS | Keys | Algorithms | Outcome |
|---|---|---|---|---|
| . | trust_anchor | 20326, 38696 | 8, 8 | Verified |
| io. | present | 38690 | 8 | Verified |
| send21.io. | absent | Unsigned (proven) parent-signed NSEC/NSEC3 proves an unsigned delegation |
Authentication Enforced and verified
The endpoint asked for a token and published valid RFC 9728 metadata describing how to get one.
| Result | Enforced and verified |
|---|---|
| Enforced | On tool calls |
| HTTP status | 200 |
WWW-Authenticate challenge Bearer resource_metadata="https://send21.io/.well-known/oauth-protected-resource/mcp", scope="drafts:read drafts:write addressbook:read addressbook:write"
Bearer resource_metadata="https://send21.io/.well-known/oauth-protected-resource/mcp", scope="drafts:read drafts:write addressbook:read addressbook:write"| Header | Value |
|---|---|
| strict-transport-security | max-age=63072000; includeSubDomains |
| content-security-policy | default-src 'none'; frame-ancestors 'none' |
| x-content-type-options | nosniff |
| x-frame-options | DENY |
| referrer-policy | no-referrer |
| permissions-policy | camera=(), microphone=(), geolocation=() |
Protected resource metadata
| Document | https://send21.io/.well-known/oauth-protected-resource/mcp |
|---|---|
| Retrieved | Yes |
| Resource | https://send21.io/mcp |
| Authorisation server | https://send21.io |
Background: How OAuth 2.1 works in the 2026 MCP spec →
Transports 2 probes
| Transport | URL | Outcome | Status | Location |
|---|---|---|---|---|
| streamable-http | https://send21.io/mcp | Verified | 200 | |
| http (plaintext) | http://send21.io/mcp | HTTPS enforced | 301 | https://send21.io/mcp |
The tools this component advertises to a client, with an estimated token cost for each. Expand a tool to see its parameters and schema. The per-tool counts are indicative and are not scored directly; the schema's total context footprint is one signal in Schema Quality & AI Usability. A tool's description is untrusted text the model reads on every call, which is what makes this list a security surface and not just an inventory: how tool poisoning works →
create_account Create send21 account for owner ~222
Create a send21 account for your human owner, without a key. The owner gets an email with a link to take the account over; until they do, nothing can be created. Returns a bootstrap API key ONCE (save it and send it as Authorization: Bearer on every later call; reconnect this MCP client with it). The key can read, propose addresses and check get_account_status; it can create pay links only after the owner took the account over and approved a receiving address you proposed. Agents onboard themselves; humans approve where the money lands. If the email already has an account, ask the owner for an API key instead.
| Name | Type | Req | Description |
|---|---|---|---|
| agentName | string|null | – | Your name as the owner will see it: letters, digits, spaces and . _ - ( ), at most 50 |
| intendedUse | string|null | – | What you will use the account for, shown to the owner (max 300 characters) |
| ownerEmail | string | yes | The human owner's email address (not yours); they receive the link to take the account over |
No output schema declared.
No examples provided.
create_draft Create payment draft ~474
Create a non-custodial payment draft (you are the SENDER paying a receiver address). Amount is either exact base units (sats for BTC, micro-units for stablecoins, lamports for SOL, gwei for ETH) via amountBaseUnits, or fiat-pegged via fiatCurrency+fiatAmount with the exchange rate locked at creation. Returns the draft incl. id, amounts, fee, and status. Funds move only when the sender signs in their own wallet. send21 never holds keys. On accounts with the policy ApprovedOnly the receiver must be an address the owner approved (422 address_not_approved otherwise). Requires scope drafts:write.
| Name | Type | Req | Description |
|---|---|---|---|
| amountBaseUnits | integer|null | – | Exact amount in base units (sats / micro-units / lamports / gwei); omit when using fiat pricing |
| currency | string|null | – | Asset: Btc (default), Usdc, Usdt, Eurc, Sol (native SOL on Solana), or Eth (native ETH on Ethereum, Base, Arbitrum) |
| fiatAmount | number|null | – | Fiat amount; requires fiatCurrency |
| fiatCurrency | string|null | – | Fiat currency code for fiat-pegged amount, e.g. USD |
| idempotencyKey | string|null | – | Idempotency key. A retry with the same key and the same parameters returns the original draft; the same key with another receiver, amount, currency or network is refused (422) and creates nothing |
| memo | string|null | – | Free-text memo shown on the draft (max 500 chars) |
| network | string | yes | Network: Mainnet, Solana, Ethereum, Base, Arbitrum, Polygon (test: Testnet4, Signet, Regtest, SolanaDevnet, EthereumSepolia, BaseSepolia, ArbitrumSepolia, PolygonAmoy) |
| receiverAddress | string | yes | Receiver address (Bitcoin bc1..., Solana base58, or 0x... for Ethereum, Base, Arbitrum and Polygon) |
| shortfallAbsorbUpToPercent | number|null | – | Accept short payments automatically when they are at most this percent below the amount (0 to 10); the receiver absorbs the difference. Overpayments always wait for a human. |
No output schema declared.
No examples provided.
create_payment_request Create pay link ~484
Create a payment request / checkout pay link (you are the RECEIVER asking to get paid). Price in any of 161 fiat currencies; the payer opens the returned payPath, picks one of the offered currencies (rate locks then), and pays a single QR-scannable transfer straight to your address. On accounts with the policy ApprovedOnly (see get_account_status) every address must be one of the owner's approved receiving addresses; otherwise the answer is 422 address_not_approved and nothing is created (propose it with propose_receiving_address). Requires scope drafts:write.
| Name | Type | Req | Description |
|---|---|---|---|
| declineNote | string|null | – | What happens if the payer does not pay (plain text, max 200 chars). Shown on the pay page under the amount as "If you don't pay:". Use it when handing an over-budget purchase to a human, e.g. "The or… |
| expiryHours | integer|null | – | Hours until the request expires (default 24) |
| fiatAmount | number | yes | Amount in the fiat currency |
| fiatCurrency | string | yes | Fiat currency the request is priced in, e.g. USD, EUR, SEK |
| idempotencyKey | string|null | – | Idempotency key. A retry with the same key and the same parameters returns the original request; the same key with another amount, currency or address is refused (422) and creates nothing |
| memo | string|null | – | Message shown to the payer (max 500 chars) |
| options | array | yes | Currencies the payer may choose from, each with your receiving address |
| orderId | string|null | – | Your own order/reference id, echoed in webhooks for reconciliation |
| reuseOpenForOrder | boolean|null | – | True: if an open, unexpired request with the same orderId exists, return it instead of creating a second pay link for the same order (only when it asks for the same amount, currency and addresses). R… |
| shortfallAbsorbUpToPercent | number|null | – | Accept short payments automatically when they are at most this percent below the price (0 to 10); the receiver absorbs the difference. Overpayments always wait for a human. Omit to have every differi… |
No output schema declared.
No examples provided.
get_account_status Get account status ~61
What stands between you and a live pay link: whether the owner's email is confirmed, the receiving-address policy, how many addresses are approved or waiting for approval, unsettled fees, your key's scopes, and the next steps. Requires scope drafts:read.
Input schema present but exposes no named parameters.
No output schema declared.
No examples provided.
get_draft Get payment draft ~44
Get a payment draft by id, including amounts, fee, quote, and status. Requires scope drafts:read.
| Name | Type | Req | Description |
|---|---|---|---|
| draftId | string | yes | Draft id (GUID) |
No output schema declared.
No examples provided.
get_draft_status Get draft status ~105
Lightweight status snapshot of a draft: status (AwaitingPayment/Seen/Confirmed/Expired/Cancelled), paying txid, confirmations, and reviewState when a transfer with a different amount arrived (pending = needs the receiver's decision and the draft is not paid; accepted; rejected; unresolved = the draft expired while undecided, the money is with the receiver). Cheap to poll. Requires scope drafts:read.
| Name | Type | Req | Description |
|---|---|---|---|
| draftId | string | yes | Draft id (GUID) |
No output schema declared.
No examples provided.
get_fee_schedule Get fee schedule ~38
Get the public send21 fee schedule: tiered percent by payment size in USD, min/max fee, and dust limit. No authentication needed.
Input schema present but exposes no named parameters.
No output schema declared.
No examples provided.
get_payment_request Get pay link ~105
Get a payment request by id: status (Open/Completed/Cancelled/Expired), pay path, offered currencies, and the underlying draft once the payer committed. Includes changeSignals and changeNotes: what is unusual compared with the account's paid payments (new_address, new_asset, unusual_amount), the same lines the payer sees on the pay page; empty when nothing is unusual. Requires scope drafts:read.
| Name | Type | Req | Description |
|---|---|---|---|
| paymentRequestId | string | yes | Payment request id (GUID) |
No output schema declared.
No examples provided.
get_rate Get exchange rate ~115
Get the current exchange rate for an asset in a fiat currency (rate = fiat units per 1 whole asset unit, with source provenance). Assets: Btc, Usdc, Usdt, Eurc, Sol, Eth. 161 ISO 4217 fiat currencies are supported. Requires an API key.
| Name | Type | Req | Description |
|---|---|---|---|
| asset | string | yes | Asset: Btc, Usdc, Usdt, Eurc, Sol, or Eth |
| fiatCurrency | string | yes | Fiat currency code, e.g. USD, EUR, SEK |
No output schema declared.
No examples provided.
get_transaction_template Get wallet payment instructions ~113
Get the transaction template for an on-chain draft: every output to pay, plus walletcreatefundedpsbt arguments and a pay-to-many CSV on Bitcoin, or payment URIs (and calldata on EVM chains) on Solana, Ethereum, Base, Arbitrum and Polygon. The sender's own wallet funds, reviews and signs it; send21 contains no signing code. Not for Lightning drafts (pay their invoice). Requires scope drafts:read.
| Name | Type | Req | Description |
|---|---|---|---|
| draftId | string | yes | Draft id (GUID) |
No output schema declared.
No examples provided.
list_address_book List address book ~45
List the account's saved addresses (label, address, network, direction: Sending = recipients the owner pays, Receiving = the owner's own addresses). Requires scope addressbook:read.
Input schema present but exposes no named parameters.
No output schema declared.
No examples provided.
list_draft_quotes List draft quotes ~78
List every quote (rate lock) of a fiat-priced draft, oldest first. Quotes never change; a re-quote adds a new one with its own id. Each has a sha256 (RFC 8785 JCS + SHA-256). Requires scope drafts:read.
| Name | Type | Req | Description |
|---|---|---|---|
| draftId | string | yes | Draft id (GUID) |
No output schema declared.
No examples provided.
propose_receiving_address Propose receiving address ~224
Propose an address for the owner to approve: one of the owner's own receiving addresses (for pay links) or the address of someone the owner pays (for drafts). It is saved unapproved and the owner gets an email. On accounts with the policy ApprovedOnly, API keys can only use approved addresses, and only the owner can approve one, signed in to the send21 app with a passkey or authenticator code. No key can approve an address. Requires scope addressbook:write.
| Name | Type | Req | Description |
|---|---|---|---|
| address | string | yes | The address, or for BTC over Lightning the Lightning address (name@wallet.com) |
| direction | string|null | – | Receiving (default): the owner's own address, for pay links. Sending: someone the owner pays, for drafts. |
| label | string | yes | A label the owner will recognise, e.g. "My Phantom wallet" (unique per account) |
| network | string | yes | Network the address lives on: Mainnet (Bitcoin, also for Lightning addresses), Solana, Ethereum, Base, Arbitrum or Polygon |
No output schema declared.
No examples provided.
submit_lightning_proof Submit Lightning payment proof ~120
Confirm a paid Lightning draft with its proof of payment: the 64-character preimage the paying wallet shows after a Lightning payment. Needed for drafts with a pasted bolt11 invoice, and for Lightning addresses whose provider does not report payments. send21 checks that SHA-256 of the preimage equals the invoice's payment hash; the draft then confirms within about 30 seconds. Requires scope drafts:write.
| Name | Type | Req | Description |
|---|---|---|---|
| draftId | string | yes | Draft id (GUID) |
| preimage | string | yes | Payment preimage, 64 hex characters |
No output schema declared.
No examples provided.
How do I install the send21 MCP server?
send21 is a hosted endpoint at https://send21.io/mcp, so there is nothing to install locally. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.
remote · send21.io
claude mcp add --transport http send21io-mcp 'https://send21.io/mcp'
What is the send21 MCP server?
send21 is an MCP server listed in the public MCP registry as io.github.send21io/mcp. Crypto pay links and API for people and AI agents. BTC, Lightning, USDC, USDT, EURC, SOL, ETH. This page covers its hosted endpoint (https://send21.io/mcp).
Is the send21 MCP server safe to use?
send21 scores 95 out of 100 on VerifyMCP. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.
What tools does the send21 MCP server expose?
send21 exposes 14 tools: get_transaction_template, get_fee_schedule, create_payment_request, propose_receiving_address, get_account_status, and 9 more. Their descriptions and schemas cost roughly 2,228 tokens of context every time the server is loaded.
Does the send21 MCP server require authentication?
Yes. send21 asked us for credentials when we connected, so you will need to authorise it in your MCP client before it can do anything.
Is the send21 MCP server still maintained?
send21 is still listed as active in the MCP registry. We last reached this channel on 5 November 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.