CLOSUM API
Agent-ready OpenAPI document · curated by JenticMarketingMarketing AutomationapiKey40 EndpointsREST
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For Agents
Manage leads, contacts, tags, and email templates in Closum, send templated emails, and wire up automation webhooks.
Use for: I want to add a new lead with a follow-up note, Tag a contact by email address, Send an email template to a specific contact, List all contacts in the database
Not supported: Does not handle payment processing, e-commerce orders, or paid ad management - use for SMB inbound marketing, lead capture, tagging, and templated email sends only.
Jentic publishes the only available OpenAPI specification for CLOSUM API, keeping it validated and agent-ready. Closum is an inbound marketing platform aimed at small and medium businesses, covering landing pages, newsletters, SMS marketing, and lightweight CRM. The v2 REST API exposes 40 operations across leads, contacts, tags, custom fields, email templates, automations, and webhooks. Authentication is an API key passed as a query parameter.
Install Jentic One Beta
Connect the CLOSUM API to your agent
Jentic One is a self-hosted execution layer for AI agents. It lets your agent call the CLOSUM API, or any other public or private API you need. You set the rules, the agent never sees your credentials, and every call is logged.
Two steps, two machines. Install the instance in a safe environment, then register your agent from wherever it runs.
1
Step 1: Jentic One Host machine
# On the machine that will host your Jentic One instance:
curl -fsSL "https://jentic.com/install.sh?src=apis&api=%2Fapis%2Fclosum.com%2Fclosum" | sh2
Step 2: Agent machine
# On the machine where your agent runs (keep this separate from the instance):
curl -fsSL "https://jentic.com/install.sh?src=apis&api=%2Fapis%2Fclosum.com%2Fclosum" | sh
jentic register # connects your agent to your Jentic One instanceJentic One is in public beta. The setup above keeps your agent separate from the instance, which is what you want before using real credentials: an agent running as the same OS user as Jentic One can read its stored keys directly. Just evaluating? A single local install is fine to start. See the secure deployment guide for the tiers.
Capabilities
What an agent can do with CLOSUM API.
Create and update leads with notes attached for sales handoff
Add and remove tags on contacts and leads by id or by email
List and edit custom contact fields used for segmentation
Send transactional emails by referencing a saved email template id
Create and update email templates programmatically
Register webhooks to react to lead and contact events
Use Cases
Patterns agents use CLOSUM API for, with concrete tasks.
★ Form-to-CRM Lead Capture
SMB marketers pull leads in from landing pages, webinars, and ads and need them in Closum within seconds. POST /lead/add/ creates the lead, POST /lead/add-note/{lead_id} attaches the source context, and POST /contact-tag/add-lead-tag/{lead_id} applies a campaign tag. The flow eliminates the manual CSV upload step and keeps source attribution intact.
Create a lead with email maria@example.com and name 'Maria Lopez', attach a note 'Source: Q3 Webinar', and tag with 'Webinar-Q3'.
Tag-Based Segmentation by Email
Closum's PUT /lead/edit-by-email and POST /contact-tag/add-tag-by-email/ endpoints let an agent enrich and segment contacts using only the email address as a key - useful when integrating with external sources that do not expose Closum ids. Agents can sync ESP-style tags from external systems without resolving ids first.
Apply the tag 'High-Intent' to the contact whose email is jess@example.com and remove the tag 'Newsletter-Only'.
Templated Transactional Sends
POST /email-template/send/{template_id} fires a saved template against a recipient, while POST /email-template/create/ and /email-template/update/ keep the template library current. This lets ops teams treat Closum like a transactional sender for a small set of recurring templates without paying for a separate ESP.
Send template 1234 to contact_id 5678 with the variable 'first_name' set to 'Maria'.
AI Agent Marketing Concierge
Embed Closum into an AI assistant that small business owners can chat with - 'add this lead, tag them, send the welcome email'. Through Jentic, the agent searches by intent, loads the right operation, and executes against Closum. The query-string API key lives in your Jentic One instance and never enters the model context.
Search Jentic for 'add lead to closum', load the schema, and execute it for a new lead captured from a Google Form submission.
Key Endpoints
40 endpoints — jentic publishes the only available openapi specification for closum api, keeping it validated and agent-ready.
METHOD
PATH
DESCRIPTION
POST
/lead/add/
Create a lead
PUT
/lead/edit-by-email
Update a lead by email
POST
/contact/add
Create a contact
POST
/contact-tag/add-tag-by-email/
Tag a contact by email
POST
/email-template/send/{template_id}
Send a saved email template
GET
/tag/
List tags
GET
/field/
List custom contact fields
POST
/lead/add/
Create a lead
PUT
/lead/edit-by-email
Update a lead by email
POST
/contact/add
Create a contact
POST
/contact-tag/add-tag-by-email/
Tag a contact by email
POST
/email-template/send/{template_id}
Send a saved email template
GET
/tag/
List tags
GET
/field/
List custom contact fields
Why Jentic?
What agents get from Jentic-routed access to this vendor.
Setup
Wiring CLOSUM by hand means passing its API key as a query-string parameter, mapping its lead, contact, tag, and email-template endpoints, and handling retries yourself against api.closum.com/v2. Through Jentic you install once, import the CLOSUM API from the API Directory, store the API key once, and your agent calls it.
Permission scoping
CLOSUM's write targets like a contact identified by email travel in the request body rather than the URL path, so scope the agent to the operations it needs, such as adding a lead or tagging a contact by email. You choose which operations are in that set, so template sends are not included unless you add them.
Credential isolation
Your CLOSUM API key is stored once, encrypted, by your own Jentic One instance and injected as the URL parameter at execution time. It never enters the agent's prompt, logs, or context.
Intent-based discovery
Agents search Jentic by intent such as 'tag a CLOSUM contact by email', and Jentic returns the matching operation with its input schema, so the agent calls the right endpoint without browsing the reference docs.
Related APIs
Alternatives and complements available in the Jentic catalogue.
FAQs
Specific to using CLOSUM API through Jentic.
Why is there no official OpenAPI spec for CLOSUM API?
Closum does not publish an OpenAPI specification - only narrative developer docs. Jentic generates and maintains this spec so that AI agents and developers can call CLOSUM API via structured tooling. It is validated against the live API and kept up to date. Get started with Jentic One, the self-hosted execution layer.
What authentication does the Closum API use?
Closum uses an API key passed as a query parameter on each request. Generate the key from your account settings. Through Jentic, the key is stored encrypted in your Jentic One instance and appended to the URL at execution time so agents never see it.
Can I tag contacts by email address with the Closum API?
Yes. POST /contact-tag/add-tag-by-email/ accepts an email and tag pair, so you do not need to resolve the contact id first. DELETE /contact-tag/remove-tag-by-email/ does the inverse. Both are useful for syncing tags from external sources keyed on email.
What are the rate limits for the Closum API?
Closum applies plan-based rate limits, typically a few requests per second per account. Exact limits are not encoded in the spec - handle 429 responses with backoff. Jentic surfaces 429s back to the agent for clean retries.
How do I send a templated email through Jentic?
Run pip install jentic, search for 'send closum email template', load the POST /email-template/send/{template_id} schema, and execute with template_id and contact_id. Variables in the template are passed in the request body.
Does the Closum API support custom fields?
Yes. GET /field/ lists the custom contact fields configured for the account; you can then reference these fields when creating or editing contacts. This lets you persist segmentation attributes that aren't part of the default contact schema.
Can I limit what my agent is allowed to do with the Closum API?
Yes. Because you run Jentic One yourself, your own rules decide which Closum operations and credentials the agent can use. You can allow it to add leads with POST /lead/add/ and tag contacts by email with POST /contact-tag/add-tag-by-email/ while keeping template sends like POST /email-template/send/{template_id} out of scope. Since Closum's write targets, such as a contact identified by email, travel in the request body, you scope the agent by picking exactly which operations belong in its set.
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