--- title: "ESG Data APIs for ESRS and VSME Reporting: What Each Class Fills" description: "Three classes of ESG data API compared: what each can feed into an ESRS or VSME report, which datapoints stay internal, and what assurance asks for." image: https://www.fiegenbaum.solutions/hubfs/pexels-cluster-images/5902299.jpg --- [Skip to content](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#main-content) [![Fiegenbaum Solutions Logo](https://www.fiegenbaum.solutions/hubfs/Branding/Fiegenbaum-Solutions_Logo.svg) ![Fiegenbaum Solutions Logo](https://www.fiegenbaum.solutions/hubfs/Branding/Fiegenbaum-Solutions_Logo.svg)](https://www.fiegenbaum.solutions/en/?hsLang=en) - Services - [Climate Risk Assessment](https://www.fiegenbaum.solutions/en/climate-risk-analysis-for-companies) - [VSME Report](https://www.fiegenbaum.solutions/en/vsme-reporting-for-smes) - [ESG Due Diligence VCs & Series A+](https://www.fiegenbaum.solutions/en/esg-due-diligence-vcs-series-a-startups) - [Corporate Carbon Footprint](https://www.fiegenbaum.solutions/en/company-carbon-footprint-methods-tools-best-practice) - Tools - [Scope 3 Quick-Check](https://www.fiegenbaum.solutions/en/scope-3-quick-check) - [ESG Investment Quick-Check](https://www.fiegenbaum.solutions/en/esg-investment-quick-check) - [CSRD Materiality Screening](https://www.fiegenbaum.solutions/en/csrd-materiality-screening) - [Pricing](https://www.fiegenbaum.solutions/en/esg-climate-consulting-fixed-prices-carbon-footprint-vsme-due-diligence-climate-risk) - [About me](https://www.fiegenbaum.solutions/en/about-me) - [Blog](https://www.fiegenbaum.solutions/en/blog) - [Contact](https://www.fiegenbaum.solutions/en/contact) ###### 9 min read # ESG Data APIs for ESRS and VSME Reporting: What Each Class Can Actually Fill By: [Johannes Fiegenbaum](https://www.fiegenbaum.solutions/en/blog/author/johannes-fiegenbaum) on 5/23/25, 11:20 AM · Last updated October 1, 2026 [ESG Data & Metrics](https://www.fiegenbaum.solutions/en/blog/tag/esg-data-metrics) [AI & Digital Sustainability](https://www.fiegenbaum.solutions/en/blog/tag/ai-digital-sustainability) ![Office buildings in Brussels at sunset](https://www.fiegenbaum.solutions/hubfs/pexels-cluster-images/5902299.jpg) Most articles about ESG data APIs are written by the companies selling them. This one is written from the other side: what these interfaces can actually deliver into a sustainability statement, what they cannot, and what an assurance provider will ask once a figure arrives over HTTP. **Table of Contents** 1. [What an ESG API Delivers, and What It Does Not](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#what-an-esg-api-delivers) 2. [Three Classes of ESG API and What Each Can Feed](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#three-classes-of-esg-api) 3. [Which ESRS and VSME Datapoints an External API Can Actually Fill](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#which-datapoints-an-api-can-fill) 4. [Selecting and Integrating: Coverage, Auth, Licences, Failure Modes](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#selecting-and-integrating) 5. [Audit Trail: What Assurance Requires When Data Arrives via API](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#audit-trail) 6. [Frequently Asked Questions](https://www.fiegenbaum.solutions/en/blog/esg-apis-sustainability-data-management-reporting#frequently-asked-questions) ## What an ESG API Delivers, and What It Does Not An ESG API is a machine readable interface to a sustainability dataset held by someone else. You send a request identifying a company, a period and a set of fields, and structured values come back instead of a PDF and a spreadsheet. What it does not give you is the content of your own report. The figures in an [ESRS or VSME disclosure](https://www.fiegenbaum.solutions/en/blog/7-key-esg-metrics-2025?hsLang=en) are, with few exceptions, measurements of your own operations: your meters, your invoices, your payroll, your supplier contracts. No external interface holds them. An ESG API earns its place in three narrower roles. It supplies context, meaning how comparable companies report. It supplies factors and reference data you would otherwise maintain by hand. And it supplies a second opinion against which your own numbers can be checked. That is also why these figures need the same [protection against cyberattacks](https://www.fiegenbaum.solutions/en/blog/protect-esg-data-cybersecurity?hsLang=en) as any other business-critical data. Buying one to close a reporting gap is the mistake I see most often. The gap is nearly always internal. ## Three Classes of ESG API and What Each Can Feed Vendors describe their products by brand. For a purchase decision it is more useful to sort them by what leaves the endpoint, because coverage, refresh cycle and licence terms all follow from that. | Class | Typical coverage | Refresh | What it can feed | Licence constraint | | --- | --- | --- | --- | --- | | **Ratings and scores** | Listed issuers, some large private companies | Annual review plus event driven changes | Screening, peer comparison, investor questionnaires | Usually internal use only, reproduction restricted | | **Raw disclosed datapoints** | Companies that publish a report, thinning fast below mid cap | One reporting cycle behind the source | Cross checks, value chain estimates, benchmark context | Attribution and redistribution terms vary by field | | **Operational and reference data** | Grid mixes, emission factors, logistics and energy activity | Continuous to monthly, factor sets versioned | The calculation layer under your own E1 figures | Factor databases carry their own terms | ## Which ESRS and VSME Datapoints an External API Can Actually Fill The database behind my benchmark work holds more than 1,000 extracted CSRD and ESRS reports. Sorting the disclosure areas by where the number physically originates gives a clearer buying signal than any coverage headline. | Disclosure area | Where the figure originates | Can an external API fill it? | | --- | --- | --- | | Scope 1 and 2 gross emissions | Meters, fuel and electricity invoices | No. An API supplies the factor, never the consumption | | [Scope 3 categories](https://www.fiegenbaum.solutions/en/blog/science-based-targets-initiative-sbti-guide-eu-companies?hsLang=en) | Spend data, supplier disclosures, activity data | Partly. Spend factors and published supplier figures yes, primary supplier data no | | Energy consumption and mix | Meter readings, national grid mix | Partly. Grid mix yes, own consumption no | | Targets and transition plan | Board decisions, internal planning | No | | Peer and sector context | Reports published by other companies | Yes. This is the one area an API genuinely owns | Read down the right hand column and the position writes itself: an external ESG API is an instrument for context and control, not a source for your own figures. It answers what other companies reported. It cannot answer what your sites consumed. ## Selecting and Integrating: Coverage, Auth, Licences, Failure Modes Five questions decide a vendor comparison, and the answers belong in writing before a trial starts: - **Coverage universe.** Not a headline company count. Ask for a hit rate against a list of your own suppliers or portfolio companies. - **Provenance per field.** Reported, estimated or modelled, flagged at field level. A feed that cannot separate the three cannot be used in a report. - **Refresh cycle and reporting year lag.** Not how often you may call the endpoint, but how old the underlying disclosure is when you get it. - **Authentication and limits.** OAuth 2.0 or key based, what the rate limit is, and what the response looks like when you hit it. - **Licence and redistribution.** Rating and score data bought via API can usually be analysed internally but not reproduced in a published sustainability report. That clause sits in the terms, not the product page. Four failure modes come from building reporting software rather than buying it. Schema drift, where a field is renamed or nested one level deeper and a pipeline that ran for months quietly stops populating a column. Emission factor versioning, where the provider updates its factor set mid year and last quarter's figures no longer reproduce. Unit and boundary mismatches, tonnes against kilogrammes, market based against location based, financial year against calendar year. And silent nulls, a missing value returned as zero, which is the one that reaches the report unnoticed. Pin the schema version, store the factor version with every calculated figure, and treat null and zero as different values from the first line of code. General-purpose AI assistants add a fifth, confident answers without a source, which is why [ChatGPT, Claude and Perplexity in ESG reporting](https://www.fiegenbaum.solutions/en/blog/ai-tools-climate-risk-analysis-perplexity-chatgpt-claude?hsLang=en) need a human check on every figure. ## Audit Trail: What Assurance Requires When Data Arrives via API An assurance provider treats an API sourced figure exactly as it treats one typed into a spreadsheet. It wants to see where the number came from and that it has not changed since. Automation does not remove that requirement, it moves it into your logs. Retain per figure: - Timestamp of request and response, not the date the report was compiled. - The raw response, stored unmodified, next to the transformed value that entered the report. - The provider's methodology or factor version in force at the time of the call. - Every transformation between response and disclosed figure: unit conversion, aggregation, restatement. - Access records, meaning who could change the pipeline and who did. - The provider's restatement policy, and any restatement affecting a figure you already published. An audit trail that exists only in a production database is not one. Teams that get this right build it before the first production call, not during the [first assurance engagement](https://www.fiegenbaum.solutions/en/blog/esg-reporting-requirements-eu-what-companies-must-know?hsLang=en). One position runs underneath all of this. Automated and AI derived ESG data is a starting point, not an audit proof result. A model that infers a supplier’s emissions from sector averages returns a number with no traceable path back to a meter reading or an invoice. That is why a vendor score cannot be dropped into an ESRS disclosure: assurance does not test whether a figure looks plausible, it tests whether it can be reconstructed. Machine generated values pass that test only where the inputs, the method version and the human review that accepted them are all on record. ## Frequently Asked Questions Is there a free ESG API, and what do free tiers actually cover? Free tiers exist. They typically cover a small universe of large listed issuers, a reduced field set and a low call limit. Enough for a proof of concept, rarely enough for a reporting cycle. What is the difference between an ESG ratings API and a raw datapoint API? A ratings API returns a score, an opinion produced by a methodology you cannot audit. A raw datapoint API returns figures a company published itself. Only the second belongs anywhere near your own disclosure. Do these APIs cover private companies and SMEs? Mostly not. Coverage follows disclosure obligations, so listed issuers are well covered while smaller suppliers are thin or modelled. For value chain data, expect to ask suppliers directly, ideally along a [VSME question set](https://www.fiegenbaum.solutions/en/blog/efrag-vsme-standard-guide-smes-sustainability-competitiveness?hsLang=en) they can answer once and reuse. Can data pulled from a vendor API be republished in a sustainability report? Often not. Rating and score licences commonly permit internal analysis and prohibit reproduction in a published document. Check the redistribution clause before designing a table around the data. Next step Turn climate risk or ESG data into a decision? In a 30-minute intro call we map where your biggest lever is, with no obligation. [Book an intro call](https://www.fiegenbaum.solutions/en/contact?hsLang=en) ![Johannes Fiegenbaum](https://www.fiegenbaum.solutions/hubfs/Johannes_07-modified.png) ### Johannes Fiegenbaum ESG and sustainability consultant based in Hamburg, specialised in VSME reporting and climate risk analysis. Has supported 300+ projects for companies and financial institutions, from mid-sized manufacturers to major banks and insurers. [More about](https://www.fiegenbaum.solutions/en/about-me?hsLang=en) Related articles ## You may also like ### [ESG Data & Metrics ESG Data Storytelling: Build Credible Narratives for Investors ESG storytelling is the practice of turning what a company actually discloses into a narrative that an investor, a customer or an auditor can follow. The thing that decides ... 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