Silmaril

Silmaril is a Y Combinator-backed runtime security company that builds an AI application firewall for agentic systems. The Silmaril Firewall classifies prompts, retrieved context, tool calls, tool responses, model output, and accumulated execution state before harmful outcomes materialize, returning a benign/malicious prediction plus a primary-outcome classification across secret exposure, information disclosure, control abuse, system compromise, and service disruption. It ships first-party TypeScript, Python, Go, and Java SDKs, LiteLLM and Vercel AI gateway guardrails, LangChain/LangGraph handlers, and agent plugins for Codex, Claude Code, OpenClaw, and Hermes, plus a hosted read-only MCP evidence server. Offered as managed and customer-controlled self-hosted container deployments.

Silmaril is listed with 1 API on the APIs.io network. Tagged areas include Company, AI Security, AI Firewall, Prompt Injection, and Agent Security.

Silmaril’s developer surface includes documentation, API reference, getting-started guide, support, authentication, changelog, and 18 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

34.4/100 thin ▬ flat Agent 30/100 agent ready Front door AI 6/6 dominant Heartbeat 100/100 alive saas Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

1 API 1 MCP Servers

Company AI Security AI Firewall Prompt Injection Agent Security Runtime Security Guardrails MCP LLM Security Developer Tools

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 34.4/100 · thin

Contract Quality 0.0 / 21

Developer Ergonomics 10.5 / 17

Access Clarity 3.6 / 17

Operational Transparency 4.9 / 11

Contract Governance 1.9 / 10

Discoverability 6.4 / 9

Regulatory Posture 4.6 / 15

Agent readiness — 30/100 · agent ready

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 12 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 8 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 6 / 6

Protected Resource Metadata 5 / 5

Registration Without a Human 6 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

Machine-Readable Contract +18 pts — api_specs includes an OpenAPI document
Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Rate-Limit Signaling +7 pts — OpenAPI responses document X-RateLimit-* / RateLimit headers (verified), else a rate_limits artifact or RateLimits link (documented)
Request/Response Examples +7 pts — share of operations carrying request/response examples; else an Examples / Code Samples link

7 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Contract Quality scores 0.0 — up to +25.0 composite points
Access Clarity scores 21.1 — up to +15.8 composite points
Contract Governance scores 18.2 — up to +9.8 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/silmaril/apis.yml: open an issue on github.com/api-evangelist/silmaril to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Standards implemented 3

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

Model Context Protocol (MCP)

measured — observed by APIs.io (verified)

OAuth 2.0 Protected Resource Metadata

measured — observed by APIs.io (verified)

Dynamic Client Registration

measured — observed by APIs.io (published)

APIs 1

Individual APIs this provider publishes, each with its own machine-readable definition.

Silmaril Firewall API

AI application firewall classify API. A Firewall client sends each sanitized classification input (user input, tool response, model output, or system prompt) with a hook label a...

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

Silmaril MCP Server

Hosted, read-only, tenant-scoped MCP server that lets an agent read Silmaril Firewall security evidence (findings, metrics, suspicious users, investigation packets, traces) from...

MCP SERVER

Security Posture 3

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Silmaril Authentication

apiKey/oauth2 · 2 schemes

SECURITY

Silmaril Domain Security

TLSv1.3 · HSTS

SECURITY

Silmaril Vulnerability Disclosure

contact published

SECURITY

Resources

Get Started 2

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

GettingStarted

GettingStarted

Documentation 2

Reference material describing how the API behaves

Documentation

Documentation

APIReference

APIReference

Agent Surfaces 2

MCP servers, agent skills, and machine-readable catalogs

LLMsTxt

LLMsTxt

MCPServer

MCPServer

Design & Contract 5

Pagination, idempotency, versioning, errors, and events

Conventions

ErrorCatalog

Lifecycle

Conformance

DataModel

Build 3

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

GitHubOrganization

Packages

Packages

SDKs

SDKs

Access & Security 4

Authentication, authorization, and security posture

Authentication

Authentication

Security

Security

VulnerabilityDisclosure

VulnerabilityDisclosure

DomainSecurity

DomainSecurity

Operate 3

Status, limits, changes, and where to get help

Support

Support

StatusPage

StatusPage

ChangeLog

ChangeLog

Commercial 2

Pricing, plans, and the legal terms of use

TermsOfService

TermsOfService

PrivacyPolicy

PrivacyPolicy

Company 1

The organization behind the API

Website

Website

Source (apis.yml)

aid: silmaril
name: Silmaril
description: Silmaril is a Y Combinator-backed runtime security company that builds an AI application firewall for agentic
  systems. The Silmaril Firewall classifies prompts, retrieved context, tool calls, tool responses, model output, and accumulated
  execution state before harmful outcomes materialize, returning a benign/malicious prediction plus a primary-outcome classification
  across secret exposure, information disclosure, control abuse, system compromise, and service disruption. It ships first-party
  TypeScript, Python, Go, and Java SDKs, LiteLLM and Vercel AI gateway guardrails, LangChain/LangGraph handlers, and agent
  plugins for Codex, Claude Code, OpenClaw, and Hermes, plus a hosted read-only MCP evidence server. Offered as managed and
  customer-controlled self-hosted container deployments.
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: false
  label: Hosted service · you call their endpoint
  confidence: medium
  source:
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - security
  generated: '2026-11-06'
  method: derived
image: https://www.silmaril.dev/icon.svg
url: https://raw.githubusercontent.com/api-evangelist/silmaril/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- y-combinator
x-tier: stub
x-tier-reason: portfolio-lead
x-enrichment:
  date: '2026-07-21'
  status: enriched
  artifacts_added: 13
  pass: local-v1
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-07-21'
tags:
- Company
- AI Security
- AI Firewall
- Prompt Injection
- Agent Security
- Runtime Security
- Guardrails
- MCP
- LLM Security
- Developer Tools
apis:
- name: Silmaril Firewall API
  description: AI application firewall classify API. A Firewall client sends each sanitized classification input (user input,
    tool response, model output, or system prompt) with a hook label and optional tool name to a tenant-issued classify endpoint,
    and receives a prediction (BENIGN/MALICIOUS), a primary outcome, and score/threshold data. Credentials and the classify
    endpoint are issued by Silmaril (not self-serve). A companion hosted, read-only MCP evidence server exposes firewall findings
    to agents.
  humanURL: https://silmaril.dev/docs
  baseURL: https://firewall-mcp.silmaril.dev
  tags:
  - AI Firewall
  - Runtime Security
  - Prompt Injection
  properties:
  - type: Documentation
    url: https://silmaril.dev/docs
  - type: APIReference
    url: https://silmaril.dev/docs
common:
- type: Website
  url: https://www.silmaril.dev/
- type: DeveloperPortal
  url: https://silmaril.dev/docs
- type: Documentation
  url: https://silmaril.dev/docs
- type: APIReference
  url: https://silmaril.dev/docs
- type: GettingStarted
  url: https://silmaril.dev/docs
- type: GitHubOrganization
  url: https://github.com/Silmaril-Security
- type: Support
  url: https://cal.com/silmaril/30min
- type: StatusPage
  url: https://silmaril.dev/status
- type: TermsOfService
  url: https://silmaril.dev/terms
- type: PrivacyPolicy
  url: https://silmaril.dev/privacy
- type: LLMsTxt
  url: llms/silmaril-llms.txt
- type: Packages
  url: packages/silmaril-packages.yml
- type: SDKs
  url: packages/silmaril-packages.yml
- type: MCPServer
  url: mcp/silmaril-mcp.yml
- type: Authentication
  url: authentication/silmaril-authentication.yml
- type: Conventions
  url: conventions/silmaril-conventions.yml
- type: ErrorCatalog
  url: errors/silmaril-error-codes.yml
- type: ChangeLog
  url: changelog/silmaril-changelog.yml
- type: Lifecycle
  url: lifecycle/silmaril-lifecycle.yml
- type: Conformance
  url: conformance/silmaril-conformance.yml
- type: DataModel
  url: data-model/silmaril-data-model.yml
- type: Security
  url: security/silmaril-vulnerability-disclosure.yml
- type: VulnerabilityDisclosure
  url: security/silmaril-vulnerability-disclosure.yml
- type: DomainSecurity
  url: security/silmaril-domain-security.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io

Silmaril API — frequently asked questions

Does Silmaril have an API?

Yes. APIs.io lists 1 API from Silmaril, including Silmaril Firewall API.

How do I authenticate with the Silmaril API?

Silmaril documents its authentication (apiKey/oauth2 · 2 schemes). The details are profiled on APIs.io as Silmaril Authentication.

Does Silmaril have an MCP server?

Yes. APIs.io lists 1 MCP server for Silmaril: Hosted, read-only, tenant-scoped MCP server that lets an agent read Silmaril Firewall security evidence (findings, metrics, suspicious users, investigation packets, traces) from an authorized tenant.

Is the Silmaril API ready for AI agents?

Silmaril has a Kin Score of 34.4 out of 100 (thin) and an Agent Readiness score of 30.2 (agent-ready), scored by API Evangelist on 2026-11-06.

Work with this as data

Every provider here is available over the APIs.io API and to AI agents over MCP.

MCP server

One button, every client — Claude, Cursor, VS Code and the rest.

https://apis.io/mcp

Tools for providers

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find_providersBrowse and filter every provider in the catalog.
get_provider_artifactsEvery artifact this provider publishes, grouped by type.
get_provider_operationsEvery operation across all of their OpenAPIs — one call instead of parsing every spec.
get_provider_toolsEvery MCP tool they ship, with the operation each wraps.
get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
get_provider_ratingPRO — composite, band, trend and facet scores.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

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